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EXPERIMENTS 


WITH 


ALTERNATE  CUBRENTS 


OF 


HIGH  POTENTIAL  AND  HIGH  FREQUENCY. 


BY 


NIKOLA  TESLA. 


A  LECTURE} 

DELIVERED  BEFORE  THE 

INSTITUTION  OF  ELECTRICAL  ENGINEERS,  LONDON. 


With  a  Portrait  and  Biographical  Sketch 
of  the  Author. 


NEW  YORK  : 

The  W.  J.  Johnston  Company,  Ltd., 
167-176  Times  Building. 

1892. 


*  l 


■ 


. 


531  5 


Biographical  Sketch  of  Nikola  Tesla. 


While  a  large  portion  of  the  European  family  has  been 
surging  westward  during  the  last  three  or  four  hundred 
years, 'settling  the  vast  continents  of  America,  another,  but 
smaller,  portion  has  been  doing  frontier  work  in  the  Old 
World,  protecting  the  rear  by  beating  back  the  “unspeak¬ 
able  Turk”  and  reclaiming  gradually  the  fair  lands  that 
endure  the  curse  of  Mohammedan  rule.  For  a  long  time 
the  Slav  people — who,  after  the  battle  of  Kosovopjolje,  in 
which  the  Turks  defeated  the  Servians,  retired  to  the  con¬ 
fines  of  the  present  Montenegro,  Dalmatia,  Herzegovina 
and  Bosnia,  and  “Borderland”  of  Austria — knew  what  it 
was  to  deal,  as  our  Western  pioneers  did,  with  foes  cease¬ 
lessly  fretting  against  their  frontier  ;  and  the  races  of  these 
countries,  through  their  strenuous  struggle  against  the 
armies  of  the  Crescent,  have  developed  notable  qualities  of 
bravery  and  sagacity,  while  maintaining  a  patriotism  and 
independence  unsurpassed  in  any  other  nation. 

It  was  in  this  interesting  border  region,  and  from  among 
these  valiant  Eastern  folk,  that  Nikola  Tesla  was  born  in 
the  year  1857,  and  the  fact  that  he,  to-day,  finds  himself  in 
America  and  one  of  our  foremost  electricians,  is  striking 
evidence  of  the  extraordinary  attractiveness  alike  of  elec¬ 
trical  pursuits  and  of  the  country  where  electricity  enjoys 
ds  widest  application. 


B  X'Wb 


IV 


Mr.  Tesla’s  native  place  was  Smiljan,  Lika,  where  his 
father  was  an  eloquent  clergyman  of  the  Greek  Church, 
in  which,  by  the  way,  his  family  is  still  prominently  repre¬ 
sented.  His  mother  enjoyed  great  fame  throughout  the 
country  side  for  her  skill  and  originality  in  needlework, 
and  doubtless  transmitted  her  ingenuity  to  Nikola;  though 
it  naturally  took  another  and  more  masculine  direction. 

The  boy  was  early  put  to  his  books,  and  upon  his  father’s 
removal  to  Gospic  he  spent  four  years  in  the  public  school, 
and  later,  three  years  in  the  Real  School,  as  it  is  called. 
His  escapades  were  such  as  most  quickwitted  boys  go 
through,  although  he  varied  the  programme  on  one  oc¬ 
casion  by  getting  imprisoned  in  a  remote  mountain  chapel 
rarely  visited  for  service;  and  on  another  occasion  by  fall¬ 
ing  headlong  into  a  huge  kettle  of  boiling  milk,  just  drawn 
from  the  paternal  herds.  A  third  curious  episode  was 
that  connected  with  his  efforts  to  fly  when,  attempting  to 
navigate  the  air  with  the  aid  of  an  old  umbrella,  he  had,  as 
might  be  expected,  a  very  bad  fall,  and  was  laid  up  for 
six  weeks. 

About  this  period  he  began  to  take  delight  in  arithmetic 
and  physics.  One  queer  notion  he  had  was  to  work  out 
everything  by  three  or  the  power  of  three.  He  was  now 
sent  to  an  aunt  at  Cartstatt,  Croatia,  to  finish  his  studies  in 
what  is  known  as  the  Higher  Real  School.  It  was  there 
that,  coming  from  the  rural  fastnesses,  he  saw  a  steam  en¬ 
gine  for  the  first  time  with  a  pleasure  that  he  remembers 
to  this  day.  At  Cartstatt  he  was  so  diligent  as  to  compress 
the  four  years’  course  into  three,  and  graduated  in  1873. 
Returning  home  during  an  epidemic  of  cholera,  he  was 


V 


stricken  down  by  the  disease  and  suffered  so  seriously  from 
the  consequences  that  his  studies  were  interrupted  for  fully 
two  years.  But  the  time  was  not  wasted,  for  he  had  be¬ 
come  passionately  fond  of  expeiimenting,  and  as  much  as 
his  means  and  leisure  permitted  devoted  his  ener¬ 
gies  to  electrical  study  and  investigation.  Up  to  this  period 
it  had  been  his  father’s  intention  to  make  a  priest  of  him, 
and  the  idea  hung  over  the  young  physicist  like  a  very 
sword  of  Damocles.  Finally  he  prevailed  upon  his  worthy 
but  reluctant  sire  to  send  him  to  Gratz  in  Austria  to  finish 
his  studies  at  the  Polytechnic  School,  and  to  prepare 
for  work  as  professor  of  mathematics  and  physics.  At 
Gratz  he  saw  and  operated  a  Gramme  machine  for  the 
first  time,  and  was  so  struck  with  the  objections 
to  the  use  of  commutators  and  brushes  that  he  made 
up  his  mind  there  and  then  to  remedy  that  defect  in 
dynamo-electric  machines.  In  the  second  year  of  his 
course  he  abandoned  the  intention  of  becoming  a  teacher 
and  took  up  the  engineering  curriculum.  After  three  years 
of  absence  he  returned  home,  sadly,  to  see  his  father  die  ; 
but,  having  resolved  to  settle  down  in  Austria,  and  recog¬ 
nizing  the  value  of  linguistic  acquirements,  he  went  to 
Prague  and  then  to  Buda-Pesth  with  the  view  of  master¬ 
ing  the  languages  he  deemed  necessary.  Up  to  this  time 
he  had  never  realized  the  enormous  sacrifices  that  his 
parents  had  made  in  promoting  his  education,  but  he  now 
began  to  feel  the  pinch  and  to  grow  unfamiliar  with  the 

image  of  Francis  Joseph  I.  There  was  considerable  lag 

•  •  J* 

between  his  dispatches  and  the  corresponding  remittance 

from  home;  and  when  the  mathematical  expression  for 


VI 


the  value  of  the  lag  assumed  the  shape  of  an  eight  laid 
flat  on  its  back,  Mr.  Tesla  became  a  very  fair  example  of 
high  thinking  and  plain  living,  but  he  made  up  his  mind 
to  the  struggle  and  determined  to  go  through  depending 
solely  on  his  own  resources.  Not  desiring  the  fame  of  a 
faster,  he  cast  about  for  a  livelihood,  and  through  the  help 
of  friends  he  secured  a  berth  as  assistant  in  the  engineer¬ 
ing  department  of  the  government  telegraphs.  The 
salary  was  five  dollars  a  week.  This  brought  him  into 
direct  contact  with  practical  electrical  work  and  ideas, 
but  it  is  needless  to  say  that  his  means  did  not  admit 
of  much  experimenting.  By  the  time  he  had  extracted 
several  hundred  thousand  square  and  cube  roots  for  the 
public  benefit,  the  limitations,  financial  and  otherwise,  of  the 
position  had  become  painfully  apparent,  and  he  concluded 
that  the  best  thing  to  do  was  to  make  a  valuable  invention. 
He  proceeded  at  once  to  make  inventions,  but  their  value 
was  visible  only  to  the  eye  of  faith,  and  they  brought  no 
grist  to  the  mill.  Just  at  this  time  the  telephone  made  its 
appearance  in  Hungary,  and  the  success  of  that  great  in¬ 
vention  determined  his  career,  hopeless  as  the  profession 
had  thus  far  seemed  to  him.  He  associated  himself  at  once 
with  telephonic  work,  and  made  various  telephonic  inven¬ 
tions,  including  an  operative  repeater;  but  it  did  not  take 
him  long  to  discover  that,  being  so  remote  from  the  scenes 
of  electrical  activity,  he  was  apt  to  spend  time  on  aims  and 
results  already  reached  by  others,  and  to  lose  touch.  Long¬ 
ing  for  new  opportunities  and  anxious  for  the  development 
of  which  he  felt  himself  possible,  if  once  he  could  place 
himself  within  the  genial  and  direct  influences  of  the  gulf 


streams  of  electrical  thought,  he  broke  away  from  the  ties 
and  traditions  of  the  past,  and  in  1881  made  his  way  to  Paris. 
Arriving  in  that  city,  the  ardent  young  Likan  obtained  em¬ 
ployment  as  an  electrical  engineer  with  one  of  the  largest 
electric  lighting  companies.  The  next  year  lie  went  to 
Strasburg  to  install  a  plant,  and  on  returning  to  Paris 
sought  to  carry  out  a  number  of  ideas  that  had  now  ripened 
into  inventions.  About  this  time,  however,  the  remarkable 
progress  of  America  in  electrical  industry  attracted  his  at¬ 
tention,  and  once  again  staking  everything  on  a  single 
throw,  he  crossed  the  Atlantic. 

Mr.  Tesla  buckled  down  to  work  as  soon  as  he  landed  on 
these  shores,  put  his  best  thought  and  skill  into  it,  and 
soon  saw  openings  for  his  talent.  In  a  short  while  a  prop¬ 
osition  was  made  to  him  to  start  his  own  company,  and, 
accepting  the  terms,  he  at  once  worked  up  a  practical  sys¬ 
tem  of  arc  lighting,  as  well  as  a  potential  method  of  dy¬ 
namo  regulation,  which  in  one  form  is  now  known  as  the 
“  third  brush  regulation.”  He  also  devised  a  thermo-mag¬ 
netic  motor  and  other  kindred  devices,  about  which  little 
was  published,  owing  to  legal  complications.  Early  in 
1887  the  Tesla  Electric  Company  of  New  York  was  formed, 
and  not  long  after  that  Mr.  Tesla  produced  his  admirable 
and  epoch-marking  motors  for  multiphase  alternating  cur¬ 
rents,  in  which,  going  back  to  his  ideas  of  long  ago,  he 
evolved  machines  having  neither  commutator  nor  brushes. 
It  will  be  remembered  that  about  the  time  that  Mr.  Tesla 
brought  out  his  motors,  and  read  his  thoughtful  paper  be¬ 
fore  the  American  Institute  of  Electrical  Engineers,  Pro¬ 
fessor  Ferraris,  in  Europe,  published  his  discovery  of  prin- 


VIII 


ciples  analogous  to  those  ennunciated  by  Mr.  Tesla.  There 
is  no  doubt,  however,  that  Mr.  Tesla  was  an  independent 
inventor  of  this  rotary  field  motor,  for  although  anticipated 
in  dates  by  Ferraris,  he  could  not  have  known  about  Fer- 
raris’  work  as  it  had  not  been  published.  Professor  Fer¬ 
raris  stated  himself,  with  becoming  modesty,  that  he  did 
not  think  Tesla  could  have  known  of  his  (Ferraris’)  experi¬ 
ments  at  that  time,  and  adds  that  he  thinks  Tesla  was  an 
independent  and  original  inventor  of  this  principle.  With 
such  an  acknowledgment  from  Ferraris  there  can  be  little 
doubt  about  Tesla’s  originality  in  this  matter. 

Mr.  Tesla’s  work  in  this  field  was  wonderfully  timely, 
and  its  worth  was  promptly  appreciated  in  various  quarters. 
The  Tesla  patents  were  acquired  by  the  Westingliouse  Elec¬ 
tric  Company,  who  undertook  to  develop  his  motor  and  to 
apply  it  to  work  of  different  kinds.  Its  use  in  mining,  and 
its  employment  in  printing,  ventilation,  etc.,  was  described 
and  illustrated  in  The  Electrical  World  some  years  ago. 
The  immense  stimulus  that  the  announcement  of  Mr. 
Tesla’s  work  gave  to  the  study  of  alternating  current 
motors  would,  in  itself,  be  enough  to  stamp  him  as  a  leader. 

Mr.  Tesla  is  only  35  years  of  age.  He  is  tall  and  spare? 
with  a  clean-cut,  thin,  refined  face,  and  eyes  that  recall  all 
the  stories  one  has  read  of  keenness  of  vision  and  phenom¬ 
enal  ability  to  see  through  things.  He  is  an  omnivorous 
reader,  who  never  forgets;  and  he  possesses  the  peculiar 
facility  in  languages  that  enables  the  least  educated  native 
of  eastern  Europe  to  talk  and  write  in  at  least  half  a  dozen 
tongues.  A  more  congenial  companion  cannot  be  desired 
for  the  hours  when  one  “pours  out  heart  affluence  in  dis- 


IX 


cursive  talk,”  and  when  the  conversation,  dealing  at  first 
with  things  near  at  hand  and  next  to  us,  reaches  out  and 
rises  to  the  greater  questions  of  life,  duty  and  destiny. 

In  the  year  1890  he  severed  his  connection  with  the  West- 
inghouse  Company,  since  which  time  he  has  devoted  him¬ 
self  entirely  to  the  study  of  alternating  currents  of  high 
frequencies  and  very  high  potentials,  with  which  study  he 
is  at  present  engaged.  No  comment  is  necessary  on  his 
interesting  achievements  in  this  field;  the  famous  London 
lecture  published  in  this  volume  is  a  proof  in  itself.  His 
first  lecture  on  his  researches  in  this  new  branch  of  electric¬ 
ity,  which  he  may  be  said  to  have  created,  was  delivered  be¬ 
fore  the  American  Institute  of  Electrical  Engineers  on  May 
20,  1891,  and  remains  one  of  the  most  interesting  papers 
read  before  that  society.  It  will  be  found  reprinted  in  full 
in  The  Electrical  World,  July  11,  1891.  Its  publication 
excited  such  interest  abroad  that  he  received  numerous  re¬ 
quests  from  English  and  French  electrical  engineers  and 
scientists  to  repeat  it  in  those  countries,  the  result  of  which 
has  been  the  interesting  lecture  published  in  this  volume. 

The  present  lecture  presupposes  a  knowledge  of  the  for¬ 
mer,  but  it  may  be  read  and  understood  by  any  one  even 
though  he  has  not  read  the  earlier  one.  It  forms  a  sort 
cf  continuation  of  the  latter,  and  includes  chiefly  the  results 
of  his  researches  since  that  time. 


EXPERIMENTS 


WITH 

Alternate  Currents  of  High  Potential 
and  High  Frequency- 


I  cannot  find  words  to  express  how  deeply  I  feel  the 
honor  of  addressing  some  of  the  foremost  thinkers  of  the 
present  time,  and  so  many  able  scientific  men,  engineers 
and  electricians,  of  the  country  greatest  in  scientific 
achievements. 

v 

The  results  which  I  have  the  honor  to  present  before  such 
a  gathering  I  cannot  call  my  own.  There  are  among  you 
not  a  few  who  can  lay  better  claim  than  myself  on  any 
feature  of  merit  which  this  work  may  contain.  I  need  not 
mention  many  names  which  are  world-known — names  of 
those  among  you  who  are  recognized  as  the  leaders  in  this 
enchanting  science  ;  but  one,  at  least,  I  must  mention — a 
name  which  could  not  be  omitted  in  a  demonstration  of  this 
kind.  It  is  a  name  associated  with  the  most  beautiful  in¬ 
vention  ever  made  :  it  is  Crookes  ! 

When  I  was  at  college,  a  good  time  ago,  I  read,  in  a 
translation  (for  then  I  was  not  familiar  with  your  magnifi¬ 
cent  language),  the  description  of  his  experiments  on  radiant 
matter.  I  read  it  only  once  in  my  life — that  time — yet  every 


2 


detail  about  that  charming  work  I  can  remember  this  day. 
Few  are  the  books,  let  me  say,  which  can  make  such  an 
impression  upon  the  mind  of  a  student. 

But  if,  on  the  present  occasion,  I  mention  this  name  as  * 
one  of  many  your  institution  can  boast  of,  it  is  because  I 
have  more  than  one  reason  to  do  so.  For  what  I  have  to 
tell  you  and  to  show  you  this  evening  concerns,  in  a  large 
measure,  that  same  vague  world  which  Professor  Crookes 
has  so  ably  explored  ;  and,  more  than  this,  when  I  trace 
back  the  mental  process  which  led  me  to  these  advances  — 
which  even  by  myself  cannot  be  considered  trifling,  since 
they  are  so  appreciated  by  you — I  believe  that  their  real 
origin,  that  which  started  me  to  work  in  this  direction,  and 
brought  me  to  them,  after  a  long  period  of  constant  thought, 
was  that  fascinating  little  book  which  I  read  many  years 
ago. 

And  now  that  I  have  made  a  feeble  effort  to  express  my 
homage  and  acknowledge  my  indebtedness  to  him  and 
others  among  you,  I  will  make  a  second  effort,  which  I 
hope  you  will  not  find  so  feeble  as  the  first,  to  entertain 
you. 

Give  me  leave  to  introduce  the  subject  in  a  few  words. 

* 

A  short  time  ago  I  had  the  honor  to  bring  before  our 
American  Institute  of  Electrical  Engineers*  some  results 
then  arrived  at  by  me  in  a  novel  line  of  work.  I  need  not 
assure  you  that  the  many  evidences  which  I  have  received 
that  English  scientific  men  and  engineers  were  interested 

*For  Mr.  Tesla  s  American  lecture  on  this  subject  see  The  Elec¬ 
trical  World  of  July  11,  1891,  and  for  a  report  of  his  French  lee 
ture  see  The  Electrical  World  of  March  26,  1892. 


8 


in  this  work  have  "been  for  me  a  great  reward  and  encour¬ 
agement.  I  will  not  dwell  upon  the  experiments  already 
described,  except  with  the  view  of  completing,  or  more 
clearly  expressing,  some  ideas  advanced  by  me  before,  and 
also  with  the  view  of  rendering  the  study  here  presented 
self-contained,  and  my  remarks  on  the  subject  of  this  even¬ 
ing's  lecture  consistent. 

This  investigation,  then,  it  goes  without  saying,  deals  with 
alternating  currents,  and,  to  be  more  precise,  with  alter¬ 
nating  currents  of  high  potential  and  high  frequency.  Just 
in  how  much  a  very  high  frequency  is  essential  for  the  pro¬ 
duction  of  the  results  presented  is  a  question  which,  even 
with  my  present  experience,  would  embarrass  me  to  an¬ 
swer.  Some  of  the  experiments  may  be  performed  with 
low  frequencies ;  but  very  high  frequencies  are  desirable, 
not  only  on  account  of  the  many  effects  secured  by  their 
use,  but  also  as  a  convenient  means  of  obtaining,  in  the  in¬ 
duction  apparatus  employed,  the  high  potentials,  which  in 
their  turn  are  necessary  to  the  demonstration  of  most  of 
the  experiments  here  contemplated. 

Of  the  various  branches  of  electrical  investigation,  per¬ 
haps  the  most  interesting  and  immediately  the  most  promis¬ 
ing  is  that  dealing  with  alternating  currents.  The  progress 
in  this  branch  of  applied  science  has  been  so  great  in  recent 
years  that  it  justifies  the  most  sanguine  hopes.  Hardly 
have  we  become  familiar  with  one  fact,  when  novel  ex¬ 
periences  are  met  with  and  new  avenues  of  research  are 
opened.  Even  at  this  hour  possibilities  not  dreamed  of  be¬ 
fore  are,  by  the  use  of  these  currents,  partly  realized.  As 
in  nature  all  is  ebb  and  tide,  all  is  wave  motion,  so  it  seems 


4 


that  in  all  branches  of  industry  alternating  currents — elec¬ 
tric  wave  motion — will  have  the  sway. 

One  reason,  perhaps,  why  this  branch  of  science  is  being 
so  rapidly  developed  is  to  be  found  in  the  interest  which 
is  attached  to  its  experimental  study.  We  wind  a  simple 
ring  of  iron  with  coils  ;  we  establish  the  connections  to  the 
generator,  and  with  wonder  and  delight  we  note  the  effects 
of  strange  forces  which  we  bring  into  play,  which  allow  us 
to  transform,  to  transmit  and  direct  energy  at  will.  We 
arrange  the  circuits  properly,  and  we  see  the  mass  of  iron 
and  wires  behave  as  though  it  were  endowed  with  life, 
spinning  a  heavy  armature,  through  invisible  connections, 
w'th great  speed  and  power— with  the  energy  possibly  con¬ 
veyed  from  a  great  distance.  We  observe  how  the  energy 
of  an  alternating  cuirent  traversing  the  wire  manifests 
itself — not  so  much  in  the  wire  as  in  the  surrounding  space 
— in  the  most  surprising  manner,  taking  the  forms  of  heat, 
light,  mechanical  energy,  and,  most  surprising  of  all,  even 
chemical  affinity.  All  these  observations  fascinate  us,  and 
fill  us  with  an  intense  desire  to  know  more  about  the 
nature  of  these  phenomena.  Each  day  we  go  to  our  work 
in  the  hope  of  discovering, — in  the  hope  that  some  one,  no 
matter  who,  may  find  a  solution  of  one  of  the  pending  great 
problems, — and  each  succeeding  day  we  return  to  our  task 
with  renewed  ardor  ;  and  even  if  we  are  unsuccessful,  our 
work  has  not  been  in  vain,  for  in  these  strivings,  in  these 
efforts,  we  have  found  hours  of  untold  pleasure,  and  we 
have  directed  our  energies  to  the  benefit  of  mankind. 

We  may  take — at  random,  if  you  choose — any  of  the 
many  experiments  which  may  be  performed  with  alternat- 


mg  currents;  a  few  of  which  only,  and  by  no  means  the 
most  striking,  form  the  subject  of  this  evening’s  demon¬ 
stration  ;  they  are  all  equally  interesting,  equally  inciting 
to  thought. 

Here  is  a  simple  glass  tube  from  which  the  air  has  been 
partially  exhausted.  I  take  hold  of  it;  I  bring  my  body  in 
contact  with  a  wire  conveying  alternating  currents  of  high 
potential,  and  the  tube  in  my  hand  is  brilliantly  lighted. 
In  whatever  position  I  may  put  it,  wherever  I  may  move 
it  in  space,  as  far  as  I  can  reach,  its  soft,  pleasing  light  per¬ 
sists  with  undiminished  brightness. 

Here  is  an  exhausted  bulb  suspended  from  a  single  wire. 
Standing  on  an  insulated  support,  I  grasp  it,  and  a  plati¬ 
num  button  mounted  in  it  is  brought  to  vivid  incandescence. 

Here,  attached  to  a  leading  wire,  is  another  bulb,  which, 
as  I  touch  its  metallic  socket,  is  filled  with  magnificent 
colors  of  phosphorescent  light. 

Here  still  another,  which  by  my  fingers’  touch  casts  a 
shadow — the  Crookes  shadow,  of  the  stem  inside  of  it. 

Here,  again,  insulated  as  I  stand  on  this  platform,  I  bring 
my  body  in  contact  with  one  of  the  terminals  of  the  sec¬ 
ondary  of  this  induction  coil — with  the  end  of  a  wire  many 
miles  long — and  you  see  streams  of  light  break  forth  from 
its  distant  end,  which  is  set  in  violent  vibration. 

Here,  once  more,  I  attach  these  two  plates  of  wire  gauze 
to  the  terminals  of  the  coil,  I  set  them  a  distance  apart,  and 
I  set  the  coil  to  work.  You  may  see  a  small  spark  pass  be¬ 
tween  the  plates.  I  insert  a  thick  plate  of  one  of  the  best 
dielectrics  between  them,  and  instead  of  rendering  alto¬ 
gether  impossible,  as  we  are  used  to  expect,  I  aid  the  pas- 


e 


sage  of  the  discharge,  which,  as  I  insert  the  plate,  merely 
changes  in  appearance  and  assumes  the  form  of  luminous 
streams. 

Is  there,  I  ask,  can  there  be,  a  more  interesting  study 
than  that  of  alternating  currents? 

In  all  these  investigations,  in  all  these  experiments, 
which  are  so  very,  very  interesting,  for  many  years 
past — ever  since  the  greatest  experimenter  who  lec¬ 
tured  in  this  hall  discovered  its  principle — we  have  had 
a  steady  companion,  an  appliance  familiar  to  every  one,  a 
plaything  once,  a  thing  of  momentous  importance  now — 
the  induction  coil.  There  is  no  dearer  appliance  to  the 
electrician.  From  the  ablest  among  you,  I  dare  say,  down 
to  the  inexperienced  student,  to  your  lecturer,  we  all  have 
passed  many  delightful  hours  in  experimenting  with  the 
induction  coil.  We  have  watched  its  play,  and  thought 
and  pondered  over  the  beautiful  phenomena  which  it  dis¬ 
closed  to  our  ravished  eyes.  So  well  known  is  this  appa¬ 
ratus,  so  familiar  are  these  phenomena  to  every  one,  that 
my  courage  nearly  fails  me  when  I  think'  that  I  have  ven¬ 
tured  to  address  so  able  an  audience,  that  I  have  ventured 
to  entertain  you  with  that  same  old  subject.  Here  in  real¬ 
ity  is  the  same  apparatus,  and  here  are  the  same  phenom 
ena,  only  the  apparatus  is  operated  somewhat  differently, 
the  phenomena  are  presented  in  a  different  aspect.  Som( 
of  the  results  we  find  as  expected,  others  surprise  us,  bul 
all  captivate  our  attention,  for  in  scientific  investigatior 
each  novel  result  achieved  may  be  the  centre  of  a  new  de 
parture,  each  novel  fact  learned  may  lead  to  important  de 
velopments. 


r/ 


Usually  in  operating  an  induction  coil  we  have  set  up  a 
vibration  cf  moderate  frequency  in  the  primary,  either  by 
means  of  an  interrupter  or  break,  or  by  the  use  of  an  alter¬ 
nator.  Earlier  English  investigators,  to  mention  only 
Spottiswoode  and  J.  E.  H.  Gordon,  have  used  a  rapid 
break  in  connection  with  the  coil.  Our  knowledge  and 
experience  of  to-day  enables  us  to  see  clearly  why  these 
coils  under  the  conditions  of  the  tests  did  not  disclose  any, 
remarkable  phenomena,  and  why  able  experimenters 
failed  to  preceive  many  of  the  curious  effects  which  have 
since  been  observed. 

In  the  experiments  such  as  performed  this  evening,  we 
operate  the  coil  either  from  a  specially  constructed  alter¬ 
nator  capable  of  giving  many  thousands  of  reversals  of 
current  per  second,  or,  by  disruptively  discharging  a  con¬ 
denser  through  the  primary,  we  set  up  a  vibration  in  the 
secondary  circuit  of  a  frequency  of  many  hundred  thou¬ 
sand  or  millions  per  second,  if  we  so  desire;  and  in  using 
either  of  these  means  we  enter  a  field  as  yet  unexplored. 

It  is  impossible  to  pursue  an  investigation  in  any  novel 
line  without  finally  making  some  interesting  observation 
or  learning  some  useful  fact.  That  this  statement  is  appli¬ 
cable  to  the  subject  of  this  lecture  the  many  curious  and 
unexpected  phenomena  which  we  observe  afford  a  con¬ 
vincing  proof.  By  way  of  illustration,  take  for  instance 
the  most  obvious  phenomena,  those  of  the  discharge  of  the 
induction  coil. 

Here  is  a  coil  which  is  operated  by  currents  vibrating 
with  extreme  rapidity,  obtained  by  disruptively  discharg¬ 
ing  a  Leyden  jar.  It  would  not  surprise  a  student  were 


I 

8 

the  lecturer  to  say  that  the  secondary  of  this  coil  consists 
of  a  small  length  of  comparatively  stout  wire  ;  it  would  not 
surprise  him  were  the  lecturer  to  state  that,  in  spite  of  this, 
the  coil  is  capable  of  giving  any  potential  which  the  best 
insulation  of  the  turns  is  able  to  withstand  ;  but  although 
he  may  be  prepared,  and  even  be  indifferent  as  to  the  antici¬ 
pated  result,  yet  the  aspect  of  the  discharge  of  the  coil  will 
surprise  and  interest  him.  Every  one  is  familiar  with  the 
discharge  of  an  ordinary  coil ;  it  need  not  be  reproduced 
here.  But,  by  way  of  contrast,  here  is  a  form  of  discharge 
of  a  coil,  the  primary  current  of  which  is  vibrating  several 
hundred  thousand  times  per  second.  The  discharge  of  an 
ordinary  coil  appears  as  a  simple  line  or  band  of  light.  The 
discharge  of  this  coil  appears  in  the  form  of  powerful 
brushes  and  luminous  streams  issuing  from  all  points  of 
the  two  straight  wires  attached  to  the  terminals  of  the 
secondary.  (Fig.  1.) 

Now  compare  this  phenomenon  which  you  have  just 
witnessed  with  the  discharge  of  a  Holtz  or  Wimsliurst 
machine — that  other  interesting  appliance  so  dear  to  the 
experimenter.  What  a  difference  there  is  between  these 
phenomena  !  And  yet,  had  I  made  the  necessary  arrange¬ 
ments — which  could  have  been  made  easily,  were  it  not 
that  they  would  interfere  with  other  experiments — I  could 
have  produced  with  this  coil  sparks  which,  had  I  the  coil 
hidden  from  your  view  and  only  two  knobs  exposed,  even 
the  keenest  observer  among  you  would  find  it  difficult,  if  not 
impossible,  to  distinguish  from  those  of  an  influence  or  fric¬ 
tion  machine.  This  may  be  done  in  many  ways — for  instance, 
by  operating  the  induction  coil  which  charges  the  con- 


9 


\N  '“V  •-> 

denser  from  an  alternating-current  machine  of  very  low 
frequency,  and  preferably  adjusting  the  discharge  circuit 
so  that  there  are  no  oscillations  set  up  in  it.  We  then  ob 


Fig.  1.— Discharge  Between  Two  Wires  with  Frequen¬ 
cies  of  a  Few  Hundred  Thousand  per  Second. 

tain  in  the  secondary  circuit,  if  the  knobs  are  of  the  required 
size  and  properly  set,  a  more  or  less  rapid  succession  of 
sparks  of  great  intensity  and  small  quantity,  which  possess 


10 


the  same  brilliancy,  and  are  accompanied  by  the  same 
sharp  crackling  sound,  as  those  obtained  from  a  friction  or 

influence  machine. 

Another  way  is  to  pass  through  two 
primary  circuits,  having  a  common 
secondary,  two  currents  of  a  slightly 
different  period,  which  produce  in  the 
secondary  circuit  sparks  occurring  at 
comparatively  long  intervals.  But, 
even  with  the  means  at  hand  this 
evening,  I  may  succeed  in  imitating 
the  spark  of  a  Holtz  machine.  For 
this  purpose  I  establish  between  the 
terminals  of  the  coil  which  charges 
the  condenser  a  long,  unsteady  arc, 
which  is  periodically  interrupted  by 
the  upward  current  of  air  produced 
by  it.  To  increase  the  current  of  air 
I  place  on  each  side  of  the  arc,  and 
close  to  it,  a  large  plate  of  mica.  The 
condenser  charged  from  this  coil  dis¬ 
charges  into  the  primary  circuit  of  a 
second  coil  through  a  small  air  gap, 
which  is  necessary  to  produce  a  sud¬ 
den  rush  of  current  through  the  pri¬ 
mary.  The  scheme  of  connections  in 
the  present  experiment  is  indicated 
in  Fig.  2. 

G  is  an  ordinarily  constructed  alternator,  supplying  the 
primary  Pof  an  induction  coil,  the  secondary  S  of  which 


Fig.  2.— Imitating 
the  Spark  of  a 
Holtz  Machine. 


K  K 


11 


charges  the  condensers  or  jars  C  C.  The  terminals  of  the 
secondary  are  connected  to  the  inside  coatings  of  the  jars, 
the  outer  coatings  being  connected  to  the  ends  of  the  pri¬ 
mary  pp  of  a  second  induction  coil.  This  primary  p  p  has 
a  small  air  gap  a  b. 

The  secondary  s  of  this  coil  is  provided  with  kpobs  or 
spheres  K  K  of  the  proper  size  and  set  at  a  distance  suit¬ 
able  for  the  experiment. 

A  long  arc  is  established  between  the  terminals  A  B  of 
the  first  induction  coil.  M  M  are  the  mica  plates. 

Each  time  the  arc  is  broken  between  A  and  B  the  jars 
are  quickly  charged  and  discharged  through  the  primary 
p  p,  producing  a  snapping  spark  between  the  knobs  K  K. 
Upon  the  arc  forming  between  A  and  B  the  potential  falls, 
and  the  jars  cannot  be  charged  to  such  high  potential  as  to 
break  through  the  air  gap  a  b  until  the  arc  is  again  broken 
by  the  draught. 

In  this  manner  sudden  impulses,  at  long  intervals,  are 
produced  in  the  primary  p  p ,  which  in  the  secondary  s 
give  a  corresponding  number  of  impulses  of  great  intensity. 
If  the  secondary  knobs  or  spheres,  K  K,  are  of  the  proper 
size,  the  sparks  show  much  resemblance  to  those  of  a  Holtz 
machine. 

But  these  two  effects,  which  to  the  eye  appear  so  very 
different,  are  only  two  of  the  many  discharge  phenomena. 
We  only  need  to  change  the  conditions  of  the  test,  and 
again  we  make  other  observations  of  interest. 

When,  instead  of  operating  ‘the  induction  coil  as  in  the 
last  two  experiments,  we  operate  it  from  a  high  frequency 
alternator,  as  in  the  next  experiment,  a  systematic  study 


12 


of  the  phenomena  is  rendered  much  more  easy.  In  such 
case,  in  varying  the  strength  and  frequency  of  the  cur¬ 
rents  through  the  primary,  we  may  observe  five  distinct 
forms  of  discharge,  which  I  have  described  in  my  former 
paper  on  the  subject*  before  the  American  Institute  of  Elec¬ 
trical  Engineers,  May  20,  1891. 

It  would  take  too  much  time,  and  it  would  lead  us  too 
far  from  the  subject  presented  this  evening,  to  reproduce 
all  these  forms,  but  it  seems  to  me  desirable  to  show  you 
one  of  them.  It  is  a  brush  discharge,  which  is  interesting 
in  more  than  one  respect.  Viewed  from  a  near  position 
it  resembles  much  a  jet  of  gas  escaping  under  great  press¬ 
ure.  We  know  that  the  phenomenon  is  due  to  the  agita¬ 
tion  of  the  molecules  near  the  terminal,  and  we  anticipate 
that  some  heat  must  be  developed  by  the  impact  of  the 
molecules  against  the  terminal  or  against  each  other.  In¬ 
deed,  we  hnd  that  the  brush  is  hot,  and  only  a  little 
thought  leads  us  to  the  conclusion  that,  could  we  but 
reach  sufficiently  high  frequencies,  we  could  produce  a 
brush  which  would  give  intense  light  and  heat,  and  which 
would  resemble  in  every  particular  an  ordinary  flame, 
save,  perhaps,  that  both  phenomena  might  not  be  due  to 
the  same  agent — save,  perhaps,  that  chemical  affinity 
might  not  be  electrical  in  its  nature. 

As  the  production  of  heat  and  light  is  here  due  to  the  im¬ 
pact  of  the  molecules,  or  atoms  of  air,  or  something  else 
besides,  and,  as  we  can  augment  the  energy  simply  by 
raising  the  potential,  we  might,  even  with  frequencies  ob- 


*See  The  Electrical  World,  July  11, 1891, 


13 


tained  from  a  dynamo  machine,  intensify  the  action  to 
such  a  degree  as  to  bring  the  terminal  to  melting  heat. 
But  with  such  low  frequencies  we  would  have  to  deal  al¬ 
ways  with  something  of  the  nature  of  an  electric  current. 
If  I  approach  a  conducting  object  to  the  brush,  a  thin 
little  spark  passes,  yet,  even  with  the  frequencies  used  this 
evening,  the  tendency  to  spark  is  not  very  great.  So,  for 
instance,  if  I  hold  a  metallic  sphere  at  some  distance  above 
the  terminal  you  may  see  the  whole  space  between  the 
terminal  and  sphere  illuminated  by  the  streams  without 
the  spark  passing;  and  with  the  much  higher  frequencies 
obtainable  by  the  disruptive  discharge  of  a  condenser,  were 
it  not  for  the  sudden  impulses,  which  are  comparatively 
few  in  number,  sparking  would  not  occur  'even  at  very 
small  distances.  However,  with  incomparably  higher  fre¬ 
quencies,  which  we  may  yet  find  means  to  produce  effi¬ 
ciently,  and  provided  that  electric  impulses  of  such  high 
frequencies  could  be  transmitted  through  a  conductor,  the 
electrical  characteristics  of  the  brush  discharge  would  com¬ 
pletely  vanish— no  spark  would  pass,  no  shock  would  be 
felt — yet  we  would  still  have  to  deal  with  an  electric  phe¬ 
nomenon,  but  in  the  broad,  modern  interpretation  of  the 
word.  In  my  first  paper  before  referred  to  I  have  pointed 
out  the  curious  properties  of  the  brush,  and  described  the 
best  manner  of  producing  it,  but  I  have  thought  it  worth 
while  to  endeavor  to  express  myself  more  clearly  in  regard 
to  this  phenomenon,  because  of  its  absorbing  interest. 

When  a  coil  is  operated  with  currents  of  very  high  fre¬ 
quency,  beautiful  brush  effects  may  be  produced,  even  if 
the  coil  be  of  comparatively  small  dimensions.  The  ex- 


14 


perimenter  may  vary  them  in  many  ways,  and,  if  it  were 
nothing  else,  they  afford  a  pleasing  sight.  What  adds  to 
their  interest  is  that  they  may  be  produced  with  one  single 
terminal  as  well  as  with  two — in  fact,  often  better  with 
one  than  with  two. 

But  of  all  the  discharge  phenomena  observed,  the  most 
pleasing  to  the  eye,  and  the  most  instructive,  are  those  ob¬ 
served  with  a  coil  which  is  operated  by  means  of  the  dis¬ 
ruptive  discharge  of  a  condenser.  The  power  of  the 
brushes,  the  abundance  of  the  sparks,  when  the  conditions 
are  patiently  adjusted,  is  often  amazing.  With  even  a  very 
small  coil,  if  it  be  so  well  insulated  as  to  stand  a  difference 
of  potential  of  several  thousand  volts  per  turn,  the  sparks 
may  be  so  abundant  that  the  whole  coil  may  appear  a  com¬ 
plete  mass  of  fire. 

Curiously  enough  the  sparks,  when  the  terminals  of  the 
coil  are  set  at  a  considerable  distance,  seem  to  dart  in  every 
possible  direction  as  though  the  terminals  were  perfectly 
independent  of  each  other.  As  the  sparks  would  soon  de¬ 
stroy  the  insulation  it  is  necessary  to  prevent  them.  This 
is  best  done  by  immersing  the  coil  in  a  good  liquid  insula¬ 
tor,  such  as  boiled-out  oil.  Immersion  in  a  liquid  maybe 
considered  almost  an  absolute  necessity  for  the  continued 
and  successful  working  of  such  a  coil. 

It  is  of  course  out  of  the  question,  in  an  experimental  lec¬ 
ture,  with  only  a  few  minutes  at  disposal  for  the  perfor¬ 
mance  of  each  experiment,  to  show  these  discharge  phe¬ 
nomena  to  advantage,  as  to  produce  each  phenomenon  at 
its  best  a  very  careful  adjustment  is  required.  But  even 
if  imperfectly  produced,  as  they  are  likely  to  be  this  even- 


15 


ing,  they  are  sufficiently  striking  to  interest  an  intelligent 
audience. 

Before  showing  some  of  these  curious  effects  I  must,  for 
the  sake  of  completeness,  give  a  short  description  of  the 


Fig.  3.— Disruptive  Discharge  Coil. 

coil  and  other  apparatus  used  in  the  experiments  with  the 
disruptive  discharge  this  evening. 

It  is  contained  in  a  box  B  (Fig.  3)  of  thick  boards  of  hard 
wood,  covered  on  the  outside  with  zinc  sheet  Z,  which  is 


16 


carefully  soldered  all  around.  It  might  be  advisable,  in  a 
strictly  scientific  investigation,  when  accuracy  is  of  great 
importance,  to  do  away  with  the  metal  cover,  as  it  might 
introduce  many  errors,  principally  on  account  of  its  com¬ 
plex  action  upon  the  coil,  as  a  condenser  of  very  small  ca¬ 
pacity  and  as  an  electrostatic  and  electromagnetic  screen. 
When  the  coil  is  used  for  such  experiments  as  are  here 
contemplated,  the  employment  of  the  metkl  cover  offers 
some  practical  advantages,  but  these  are  not  of  sufficient 
importance  to  be  dwelt  upon. 

The  coil  should  be  placed  symmetrically  to  the  metal 
cover,  and  the  space  between  should,  of  course,  not  be  too 
small,  certainly  not  less  than,  say,  five  centimetres,  but 
much  more  if  possible;  especially  the  two  sides  of  the  zinc 
box,  which  are  at  right  angles  to  the  axis  of  the  coil, 
should  be  sufficiently  remote  from  the  latter,  as  otherwise 
they  might  impair  its  action  and  be  a  source  of  loss. 

The  coil  consists  of  two  spools  of  hard  rubber  R  R,  held 
apart  at  a  distance  of  10  centimetres  by  bolts  c  and  nuts 
n,  likewise  of  hard  rubber.  Each  spool  comprises  a  tube 
T  of  approximately  8  centimetres  inside  diameter,  and  3 
millimetres  thick,  upon  which  are  screwed  two  flanges  FF, 
24  centimetres  square,  the  space  between  the  flanges  being 
about  3  centimetres.  The  secondary,  S  S,  of  the  best 
gutta  percha-covered  wire,  has  26  layers,  10  turns  in  each, 
giving  for  each  half  a  total  of  260  turns.  The  two  halves 
are  wound  oppositely  and  connected  in  series,  the  connec¬ 
tion  between  both  being  made  over  the  primary.  This 
disposition,  besides  being  convenient,  has  the  advantage 
that  when  the  coil  is  well  balanced — that  is,  when  both  of 


17 


its  terminals  Tx  T1  are  connected  to  bodies  or  devices  of 
equal  capacity — there  is  not  much  danger  of  breaking 
through  to  the  primary,  and  the  insulation  between  the 
primary  and  the  secondary  need  not  be  thick.  In  using  the 
coil  it  is  advisable  to  attach  to  both  terminals  devices  of 
nearly  equal  capacity,  as,  when  the  capacity  of  the  termi¬ 
nals  is  not  equal,  sparks  will  be  apt  to  pass  to  the  primary. 
To  avoid  this,  the  middle  point  of  the  secondary  may  be 
connected  to  the  primary,  but  this  is  not  always  practi¬ 
cable. 

*  The  primary  P  P  is  wound  in  two  parts,  and  oppositely, 
upon  a  wooden  spool  W,  and  the  four  ends  are  led  out  of 
the  oil  through  hard  rubber  tubes  t  t.  The  ends  of  the 
secondary  Tx  Tx  are  also  led  out  of  the  oil  through  rubber 
tubes  tx  tx  of  great  thickness.  The  primary  and  second¬ 
ary  layers  are  insulated  by  cotton  cloth,  the  thickness  of 
the  insulation,  of  course,  bearing  some  proportion  to  the 
difference  of  potential  between  the  turns  of  the  different 
layers.  Each  half  of  the  primary  has  four  layers,  24  turns 
in  each,  this  giving  a  total  of  96  turns.  When  both  the 
parts  are  connected  in  series,  this  gives  a  ratio  of  conver¬ 
sion  of  about  1:2.7,  and  with  the  primaries  in  multiple, 
1 :  5.4;  but  in  operating  with  very  rapidly  alternating  cur¬ 
rents  this  ratio  does  not  convey  even  an  approximate  idea 
of  the  ratio  of  the  E.  M.  Fs.  in  the  primary  and  secondary 
circuits.  The  coil  is  held  in  position  in  the  oil  on  wooden 
supports,  there  being  about  5  centimetres  thickness  of  oil 
all  round.  Where  the  oil  is  not  specially  needed,  the  space 
is  filled  with  pieces  of  wood,  and  for  this  purpose  princi¬ 
pally  the  wooden  box  B  surrounding  the  whole  is  used. 


18 


The  construction  here  shown  is,  of  course,  not  the  best  on 
general  principles,  but  I  believe  it  is  a  good  and  convenient 
one  for  the  production  of  effects  in  which  an  excessive 
potential  and  a  very  small  current  are  needed. 

In  connection  with  the  coil  I  use  either  the  ordinary 
form  of  discharger  or  a  modified  form.  In  the  former  I 
have  introduced  two  changes  which  secure  some  advantages, 
and  which  are  obvious.  If  they  are  mentioned,  it  is  only 
in  the  hope  that  some  experimenter  may  find  them  of 
use 


Fig.  4.— Arrangement  of  Improved  Discharger  and 

Magnet. 


One  of  the  changes  is  that  the  adjustable  knobs  A  and  B 
(Fig.  4),  of  the  discharger  are  held  in  jaws  of  brass,  J  J, 
bjr  spring  pressure,  this  allowing  of  turning  them  succes¬ 
sively  into  different  positions,  and  so  doing  away  with  the 
tedious  process  of  frequent  polishing  up. 

The  other  change  consists  in  the  employment  of  a  strong 
electromagnet  N  S,  which  is  placed  with  its  axis  at  right 
angles  to  the  line  joining  the  knobs  A  and  B,  and  produces 
a  strong  magnetic  field  between  them.  The  pole  pieces  of 


10 


the  magnet  are  movable  and  properly  formed  so  as  to 
protrude  between  the  brass  knobs,  in  order  to  make  the  field 
as  intense  as  possible;  but  to  prevent  the  discharge  from 
jumping  to  the  magnet  the  pole  pieces  are  protected  by  a 
layer  of  mica,  M  M,  of  sufficient  thickness.  x  and  s.>  s., 
are  screws  for  fastening  the  wires.  On  each  side  one  of 
the  screws  is  for  large  and  the  other  for  small  wires.  L  L 
are  screws  for  fixing  in  position  the  rods  R  R,  which  sup¬ 
port  the  knobs. 

In  another  arrangement  with  the  magnet  I  take  the  dis¬ 
charge  between  the  rounded  pole  pieces  themselves,  which 
in  such  case  are  insulated  and  preferably  provided  with 
polished  brass  caps. 

The  employment  of  an  intense  magnetic  field  is  of  ad¬ 
vantage  principally  when  the  induction  coil  or  transformer 
which  charges  the  condenser  is  operated  by  currents  of 
very  low  frequency.  In  such  a  case  the  number  of  the 
fundamental  discharges  between  the  knobs  may  be  so  small 
as  to  render  the  currents  produced  in  the  secondary  unsuit¬ 
able  for  many  experiments.  The  intense  magnetic  field 
then  serves  to  blow  out  the  arc  between  the  knobs  as  soon 
as  it  is  formed,  and  the  fundamental  discharges  occur  in 
quicker  succession. 

Instead  of  the  magnet,  a  draught  or  blast  of  air  may  be 
employed  with  some  advantage.  In  this  case  the  arc  is 
preferably  established  between  the  knobs  A  B ,  in  Fig.  2 
(the  knobs  a  b  being  generally  joined,  or  entirely  done 
away  with),  as  in  this  disposition  the  arc  is  long  and  un¬ 
steady,  and  is  easily  affected  by  the  draught. 

When  a  magnet  is  employed  to  break  the  arc,  it  is  better  to 


choose  the  connection  indicated  diagrammatically  in  Fig.  5, 
as  in  this  case  the  currents  forming  the  arc  are  much  more 
powerful,  and  the  magnetic  field  exercises  a  greater  influ¬ 
ence.  The  use  of  the  magnet  permits,  however,  of  the 
arc  being  replaced  by  a  vacuum  tube,  but  I  have  encoun- 


Fig.  5.— Arrangement  with  Low-Frequency  Alter¬ 
nator  and  Improved  Discharger. 


tered  great  difficulties  in  working  with  an  exhausted 
tube. 

The  other  form  of  discharger  used  in  these  and  similar 
experiments  is  indicated  in  Figs.  6  and  7.  It  consists  of  a 
number  of  brass  pieces  c  c  (Fig.  6),  each  of  which  comprises 


Fig.  6.— Discharger  with  Multiple  Gaps. 


a  spherical  middle  portion  m  with  an  extension  e  below — 
which  is  merely  used  to  fasten  the  piece  in  a  lathe  when 
polishing  up  the  discharging  surface — and  a  column  above, 
which  consists  of  a  knurled  flange  f  surmounted  by  a 
threaded  stem  1  carrying  a  nut  n,  by  means  of  which  a 

r 


wire  is  fastened  to  the  column.  The  flange  /  conveniently 
serves  for  holding  the  brass  piece  when  fastening  the  wire, 
and  also  for  turning  it  in  any  position  when  it  becomes 
necessary  to  present  a  fresh  disharging  surface.  Two 
stout  strips  of  hard  rubber  R  R,  with  planed  grooves  g  g 
(Fig.  7)  to  fit  the  middle  portion  of  the  pieces  c  c,  serve  to 
clamp  the  latter  and  hold  them  firmly  in  position  by  means 
of  two  bolts  C  C  (of  which  only  one  is  shown)  passing 
through  the  ends  of  the  strips. 


In  the  use  of  this  kind  of  discharger  I  have  found  three 
principal  advantages  over  the  ordinary  form.  First,  the 
dielectric  strength  of  a  given  total  width  of  air  space  is 
greater  when  a  great  many  small  air  gaps  are  used  instead 
of  one,  which  permits  of  working  with  a  smaller  length  of 
air  gap,  and  that  means  smaller  loss  and  less  deterioration 
of  the  metal;  secondly  by  reason  of  splitting  the  arc  up 
into  smaller  arcs,  the  polished  surfaces  are  made  to  last 
much  longer;  and,  thirdly,  the  apparatus  affords  some 


gauge  in  the  experiments.  I  usually  set  the  pieces  by 
putting  between  them  sheets  of  uniform  thickness  at  a  cer¬ 
tain  very  small  distance  which  is  known  from  the  experi¬ 
ments  of  Sir  William  Thomson  to  require  a  certain  electro¬ 
motive  force  to  be  bridged  by  the  spark. 

It  should,  of  course,  be  remembered  that  the  sparking 
distance  is  much  diminished  as  the  frequency  is  increased. 
By  taking  any  number  of  spaces  the  experimenter  has  a 
rough  idea  of  the  electromotive  force,  and  he  finds  it  easier 
to  repeat  an  experiment,  as  he  has  not  the  trouble  of  setting 
the  knobs  again  and  again.  With  this  kind  of  discharger 
I  have  been  able  to  maintain  an  oscillating  motion  without 
any  spark  being  visible  with  the  naked  eye  between  the 
knobs,  and  they  would  not  show  a  very  appreciable  rise  in 
temperature.  This  form  of  discharge  also  lends  itself  to 
many  arrangements  of  condensers  and  circuits  which  are 
often  very  convenient  and  time-saving.  I  have  used  it 
preferably  in  a  disposition  similar  to  that  indicated  in  Fig.  2, 
when  the  currents  forming  the  arc  are  small. 

I  may  here  mention  that  I  have  also  used  dischargers 
with  single  or  multiple  air  gaps,  in  which  the  discharge 
surfaces  were  rotated  with  great  speed.  No  particular 
advantage  was,  however,  gained  by  this  method,  except 
in  cases  where  the  currents  from  the  condenser  were  large 
and  the  keeping  cool  of  the  surfaces  was  necessary,  and  in 
cases  when,  the  discharge  not  being  oscillating  of  itself,  the 
arc  as  soon  as  established  was  broken  by  the  air  current, 
thus  starting  the  vibration  at  intervals  in  rapid  succession. 
I  have  also  used  mechanical  interrupters  in  many  ways.  To 
avoid  the  difficulties  with  frictional  contacts,  the  preferred 


23 


plan  adopted  was  to  establish  the  arc  and  rotate  through  it 
at  great  speed  a  rim  of  mica  provided  with  many  holes  and 
fastened  to  a  steel  plate.  It  is  understood,  of  course,  that 
the  employment  of  a  magnet,  air  current,  or  other  inter¬ 
rupter,  produces  an-effect  worth  noticing,  unless  the  self- 
induction,  capacity  and  resistance  are  so  related  that  there 
are  oscillations  set  up  upon  each  interruption. 

I  will  now  endeavor  to  show  you  some  of  the  most  note¬ 
worthy  of  these  discharge  phenomena. 

I  have  stretched  across  the  room  two  ordinary  cotton 
covered  wires,  each  about  7  metres  in  length.  .They  are 
supported  on  insulating  cords  at  a  distance  of  about  30 
centimetres.  I  attach  now  to  each  of  the  terminals  of  the 
coil  one  of  the  wires  and  set  the  coil  in  action.  Upon  turn¬ 
ing  the  lights  off  in  the  room  you  see  the  wires  strongly 
illuminated  by  the  streams  issuing  abundantly  from  their 
whole  surface  in  spite  of  the  cotton  covering,  which  may 
even  be  very  thick.  When  the  experiment  is  performed 
under  good  conditions,  the  light  from  the  wires  is  suffici¬ 
ently  intense  to  allow  distinguishing  the  objects  in  a  room. 
To  produce  the  best  result  it  is,  of  course,  necessary  to  ad¬ 
just  carefully  the  capacity  of  the  jars,  the  arc  between  the 
knobs  and  the  length  of  the  wires.  My  experience  is  that 
calculation  of  the  length  of  the  wires  leads,  in  such  case, 
to  no  result  whatever.  The  experimenter  will  do  best  to 
take  the  wires  at  the  start  very  long,  and  then  adjust  by 
cutting  off  first  long  pieces,  and  then  smaller  and  smaller 
ones  as  he  approaches  the  right  length. 

A  convenient  way  is  to  use  an  oil  condenser  of  very 
small  capacity,  consisting  of  two  small  adjustable  metal 


24 


plates,  in  connection  with  this  and  similar  experiments. 
In  such  case  I  take  wires  rather  short  and  set  at  the  be¬ 
ginning  the  condenser  plates  at  maximum  distance.  If 
the  streams  for  the  -wires  increase  by  approach  of  the 
plates,  the  length  of  the  wires  is  about  right;  if  they  dimin¬ 
ish  the  wires  are  too  long  for  that  frequency  and  potential. 
When  a  condenser  is  used  in  connection  wTith  experiments 
with  such  a  coil,  it  should  be  an  oil  condenser  by  all  means, 
as  in  using  an  air  condenser  considerable  energy  might  be 
wasted.  The  wires  leading  to  the  plates  in  the  oil  should 
be  very  thin,  heavily  coated  with  some  insulating  com¬ 
pound,  and  provided  with  a  conducting  covering — this  pref- 
erably  extending  under  the  surface  of  the  oil.  The 
conducting  cover  should  not  be  too  near  the  terminals, 
or  ends,  of  the  wire,  as  a  park  would  be  apt  to 
jump  from  the  wire  to  it.  The  conducting  coating 
is  used  to  diminish  the  air  losses,  in  virtue  of  its  action  as 
an  electrostatic  screen.  As  to  the  size  of  the  vessel  con¬ 
taining  the  oil,  and  the  size  of  the  plates,  the  experimenter 
gains  at  once  an  idea  from  a  rough  trial.  The  size  of  the 
plates  in  oil  is,  however,  calculable,  as  the  dielectric  losses 
are  very  small. 

In  the  preceding  experiment  it  is  of  considerable  interest 
to  know  what  relation  the  quantity  of  the  light  emitted 
bears  to  the  frequency  and  potential  of  the  electric  im¬ 
pulses.  My  opinion  is  that  the  heat  as  well  as  light  effects 
produced  should  be  proportionate,  under  otherwise  equal 
conditions  of  test,  to  the  product  of  frequency  and  square 
of  potential,  but  the  experimental  verification  of  the  law, 
whatever  it  may  be,  would  be  exceedingly  difficult.  One 


25 


thing  is  certain,  at  any  rate,  and  that  is,  that  in  augment¬ 
ing  the  potential  and  frequency  we  rapidly  intensify  the 
streams  ;  and,  though  it  may  be  very  sanguine,  it  is  surely 
not  altogether  hopeless  to  expect  that  we  may  succeed  in 
producing  a  practical  ilium  in  ant  on  these  lines.  We  would 
then  be  simply  using  burners  or  flames,  in  which  there 
would  be  no  chemical  process,  no  consumption  of  material. 


Fig.  8.— Effect  Produced  by  Concentrating  Streams. 

but  merely  a  transfer  of  energy,  and  which  would,  in  all 
probability  emit  more  light  and  less  heat  than  ordinary 
flames. 

The  luminous  intensity  of  the  streams  is,  of  course,  con- 


26 


siderably  increased  when  they  are  focused  upon  a  small 
surface.  This  may  be  shown  by  the  following  experiment : 

I  attach  to  one  of  the  terminals  of  the  coil  a  wire  w  (Fig. 
8),  bent  in  a  circle  of  about  30  centimetres  in  diameter,  and 
to  the  other  terminal  I  fasten  a  small  brass  sphere  s,  the 
surface  of  the  wire  being  preferably  equal  to  the  surface  of 
the  sphere,  and  the  centre  of  the  latter  being  in  a 
line  at  right  angles  to  the  plane  of  the  wire  circle  and  pass¬ 
ing  through  its  centre.  When  the  discharge  is  established 
under  proper  conditions,  a  luminous  hollow  cone  is  formed, 
and  in  the  dark  one-half  of  the  brass  sphere  is  strongly 
illuminated,  as  shown  in  the  cut. 

By  some  artifice  or  other,  it  is  easy  to  concentrate  the 
streams  upon  small  surfaces  and  to  produce  very  strong 
light  effects.  Two  thin  wires  may  thus  be  rendered  in¬ 
tensely  luminous. 

In  order  to  intensify  the  streams  the  wires  should  be  very 
thin  and  short ;  but  as  in  this  case  their  capacity  would  be 
generally  too  small  for  the  coil — at  least,  for  such  a  one  as 
the  present — it  is  necessary  to  augment  the  capacity  to  the 
required  value,  while,  at  the  same  time,  the  surface  of  the 
wires  remains  very  small.  This  may  be  done  in  many 
ways. 

Here,  for  instance,  I  have  two  plates,  R  R ,  of  hard  rub¬ 
ber  (Fig.  9),  upon  which  I  have  glued  two  very  chin  wires 
w  w,  so  as  to  form  a  name.  The  w  ires  may  be  bare  or 
covered  with  the  best  insulation — it  is  immaterial  for  the 
success  of  the  experiment.  Well  insulated  wires,  if  any¬ 
thing,  are  preferable.  On  the  back  of  each  plate, 
indicated  by  the  shaded  portion,  is  a  tinfoil  coating 


27 


4  53/, 


\>a/ 

jljX’  *  f\f 

t  t.  The  plates  are  placed  in  line  at  a  sufficient 
distance  to  prevent  a  spark  passing  from  one  to  the 
other  wire.  The  two  tinfoil  coatings  I  have  joined  by 
a  conductor  C,  and  the  two  wires  I  presently  connect  to 
the  terminals  of  the  coil.  It  is  now  easy,  by  varying  the 
strength  and  frequency  of  the  currents  through  the  primary, 


Fig.  9.— Wires  Rendered  Intensely  Luminous. 

to  find  a  point  at  which  the  capacity  of  the  system  is  best 
suited  to  the  conditions,  and  the  wires  become  so  strongly 
luminous  that,  when  the  light  in  the  room  is  turned  off  the 
name  formed  by  them  appears  in  brilliant  letters. 

It  is  perhaps  preferable  to  perform  this  experiment  with 
a  coil  operated  from  an  alternator  of  high  frequency,  as 


28 


then,  owing  to  the  harmonic  rise  and  fall,  the  streams  are 
very  uniform,  though  they  are  less  abundant  then  when 
produced  with  such  a  coil  as  the  present.  This  experiment, 
however,  may  be  performed  with  low  frequencies,  but 
much  less  satisfactorily. 


Fig.  10.— Luminous  Discs. 

When  two  wires,  attached  to  the  terminals  of  the  coil, 
are  set  at  the  proper  distance,  the  streams  between  them 
may  be  so  intense  as  to  produce  a  continuous  luminous 
sheet.  To  show  this  phenomenon  I  have  here  two  circles, 
C  and  c  (Fig.  10),  of  rather  stout  wire,  one  being  about 


29 


80  centimetres  and  the  other  80  centimetres  in  diameter. 
To  each  of  the  terminals  of  the  coil  I  attach  one  of  the 
circles.  The  supporting  wires  are  so  bent  that  the  circles 
may  be  placed  in  the  same  plane,  coinciding  as  nearly  as 
possible.  When  the  light  in  the  room  is  turned  off  and  the 
coil  set  to  work,  you  see  the  whole  space  between  the 
wires  uniformly  filled  with  streams,  forming  a  luminous 
disc,  which  could  be  seen  from  a  considerable  distance,  such 
is  the  intensity  of  the  streams.  The  outer  circle  could  have 
been  much  larger  than  the  present  one  ;  in  fact,  with  this 
coil  I  have  used  much  larger  circles,  and  I  l  ave  been  able 
to  produce  a  strongly  luminous  sheet,  covering  an  area  of 
more  than  one  square  metre,  which  is  a  remarkable  effect 
with  this  very  small  coil  To  avoid  uncertainty,  the  circle 
has  been  taken  smaller,  and  the  area  is  now  about  0.43 
square  metre. 

The  frequency  of  the  vibration,  and  the  quickness  of 
succession  of  the  spaiks  between  the  knobs,  affect  to  a 
marked  degree  the  appearance  of  the  streams.  When  the 
frequency  is  very  low,  the  air  gives  way  in  more  or  less 
the  same  manner,  as  by  a  steady  difference  of  potential, 
and  the  streams  consist  of  distinct  threads,  generally 
mingled  with  thin  sparks,  which  probably  correspond  to  the 
successive  discharges  occurring  between  the  knobs.  But 
when  the  frequency  is  extremely  high,  and  the  arc  of  the 
discharge  produces  a  very  loud  but  smooth  sound — showing 
both  that  oscillation  takes  place  and  that  the  sparks  succeed 
each  other  with  great  rapidity — then  the  luminous  streams 
formed  are  perfectly  uniform.  To  reach  this  result  very 
small  coils  and  jars  of  small  capacity  should  be  used,  I 


30 


take  two  tubes  of  thick  Bohemian  glass,  about  5  centi¬ 
metres  in  diameter  and  20  centimetres  long.  In  each  of 
the  tubes  I  slip  a  primary  of  very  thick  copper  wire.  On 
the  top  of  each  tube  I  wind  a  secondary  of  much 
thinner  gutta-percha  covered  wire.  The  two  secondaries 
I  connect  in  series,  the  primaries  preferably  in  multiple 
arc.  The  tubes  are  then  placed  in  a  large  glass  vessel,  at 
a  distance  of  10  to  15  centimetres  from  each  other,  on  in¬ 
sulating  supports,  and„  the  vessel  is  filled  with  boiled  out 
oil,  the  oil  reaching  about  an  inch  above  the  tubes.  The 
free  ends  of  the  secondary  are  lifted  out  of  the  oil  and 
placed  parallel  to  each  other  at  a  distance  of  about  10  cen¬ 
timetres.  The  ends  which  are  scraped  should  be  dipped  in 
the  oil.  Two  four-pint  jars  joined  in  series  may  be  used  to 
discharge  through  the  primary.  When  the  necessary  ad¬ 
justments  in  the  length  and  distance  of  the  wires  above  the 
oil  and  in  the  arc  of  discharge  are  made,  a  luminous  sheet 
is  produced  between  the  wires  which  is  perfectly  smooth 
and  textureless,  like  the  ordinary  discharge  through  a 
moderately  exhausted  tube. 

I  have  purposely  dwelt  upon  this  apparently  insignificant 
experiment.  In  trials  of  this  kind  the  experimenter  arrives 
at  the  startling  conclusion  that,  to  pass  ordinary  luminous 
discharges  through  gases,  no  particular  degree  of  exhaus¬ 
tion  is  needed,  but  that  the  gas  may  be  at  ordinary  or  even 
greater  pressure.  To  accomplish  this,  a  very  high  fre¬ 
quency  is  essential;  a  high  potential  is  likewise  required, 
but  this  is  a  merely  incidental  necessity.  These  experi¬ 
ments  teach  us  that,  in  endeavoring  to  discover  novel 
methods  of  producing  light  by  the  agitation  of  atoms,  or 


31 


molecules,  of  a  gas,  we  need  not  limit  our  research  to  the 
vacuum  tube,  but  may  look  forward  quite  seriously  to  the 
possibility  of  obtaining  the  light  effects  without  the  use  of 
any  vessel  whatever,  with  air  at  ordinary  pressure. 

Such  discharges  of  very  high  frequency,  which  render 
luminous  the  air  at  ordinary  pressures,  we  have  probably 
often  occasion  to  witness  in  Nature.  I  have  no  doubt  that 
if,  as  many  believe,  the  aurora  borealis  is  produced  by 
sudden  cosmic  disturbances,  such  as  eruptions  at  the  sun’s 
surface,  which  set  the  electrostatic  charge  of  the  earth  in  an 
extremely  rapid  vibration,  the  red  glow  observed  is  not  con¬ 
fined  to  the  upper  rarefied  strata  of  the  air,  but  the  dis¬ 
charge  traverses,  by  reason  of  its  very  high  frequency,  also 
the  dense  atmosphere  in  the  form  of  a  glow ,  such  as  we  or¬ 
dinarily  produce  in  a  slightly  exhausted  tube.  If  the  fre¬ 
quency  were  very  low,  or  even  more  so,  if  the  charge  were 
not  at  all  vibrating,  the  dense  air  would  break  down  as  in 
a  lightning  discharge.  Indications  of  such  breaking  down 
of  the  lower  dense  strata  of  the  air  have  been  repeatedly 
observed  at  the  occurrence  of  this  marvelous  phenom¬ 
enon  ;  but  if  it  does  occur,  it  can  only  be  attributed  to  the 
fundamental  disturbances,  which  are  few  in  number,  for 
the  vibration  produced  by  them  would  be  far  too  rapid  to 
allow'  a  disruptive  break.  It  is  the  original  and  irregular 
impulses  which  affect  the  instruments  ;  the  superimposed 
vibrations  probably  pass  unnoticed. 

When  an  ordinary  low  frequency  discharge  is  passed 
through  moderately  rarefied  air,  the  air  assumes  a  purplish 
hue.  If  by  some  means  or  other  we  increase  the  intensity 
of  the  molecular,  or  atomic,  vibration,  the  gas  changes  to 


32 


a  white  color.  A  similar  change  occurs  at  ordinary  press¬ 
ures  with  electric  impulses  of  very  high  frequency.  If  the 
molecules  of  the  air  around  a  wire  are  moderately  agitated, 
the  brush  formed  is  reddish  or  violet ;  if  the  vibration  is 
rendered  sufficiently  intense,  the  streams  become  white. 
We  may  accomplish  this  in  various  ways.  In  the  experi¬ 
ment  before  shown  with  the  two  wires  across  the  room,  I 
have  endeavored  to  secure  the  result  by  pushing  to  a  high 
value  both  the  frequency  and  potential  ;  in  the  experiment 
with  the  thin  wires  glued  on  the  rubber  plate  I  have  con¬ 
centrated  the  action  upon  a  very  small  surface — in  other 
words,  I  have  worked  with  a  great  electric  density. 

A  most  curious  form  of  discharge  is  observed  with  such 
a  coil  when  the  frequency  and  potential  are  pushed  to  the 
extreme  limit.  To  perform  the  experiment,  every  part  of 
the  coil  should  be  heavily  insulated,  and  only  two  small 
spheres — or,  better  still,  two  sharp-edged  metal  discs  ( d  d, 
Fig.  11)  of  no  more  than  a  few  centimetres  in  diameter — 
should  be  exposed  to  the  air.  The  coil  here  used  is  immersed 
in  oil,  and  the  ends  of  the  secondary  reaching  out  of  the 
oil  are  covered  with  an  air-tight  cover  of  hard  rubb(  r  of 
great  thickness.  All  cracks,  if  there  are  any,  should  be 
carefully  stopped  up,  so  that  the  brush  discharge  cannot 
form  anywhere  except  on  the  small  spheres  or  plates 
which  are  exposed  to  the  air.  In  this  case,  since  there  are 
no  large  plates  or  other  bodies  of  capacity  attached  to  the 
terminals,  the  coil  is  capable  of  an  extremely  rapid 
vibration.  The  potential  may  be  raised  by  increasing, 
as  far  as  the  experimenter  judges  proper,  the  rate 
of  change  of  the  primary  current.  With  a  coil  not  widely 


33 


differing  from  the  present,  it  is  best  to  connect  the  two  pri¬ 
maries  in  multiple  arc;  but  if  the  secondary  should  have 
a  much  greater  number  of  turns  the  primaries  should  pref¬ 
erably  be  used  in  series,  as  otherwise  the  vibration  might 
be  too  fast  for  the  secondary.  It  occurs  under  these  con¬ 
ditions  that  misty  white  streams  break  forth  from  the 


Fig.  11.— Phantom  Streams. 


edges  of  the  discs  and  spread  out  phantom-like  into  space. 
With  this  coil,  when  fairly  well  produced,  they  are  about 
25  to  30  centimetres  long.  When  the  hand  is  held  against 
them  no  sensation  is  produced,  and  a  spark,  causing  a 
shock,  jumps  from  the  terminal  only  upon  the  hand  being 
brought  much  nearer.  If  the  oscillation  of  the  primary 


current  is  rendered  intermittent  by  some  means  or  other, 
there  is  a  corresponding  throbbing  of  the  streams,  and  now 
the  hand  or  other  conducting  object  may  be  brought  in 
still  greater  proximity  to  the  terminal  without  a  spark 
being  caused  to  jump. 

Among  the  many  beautiful  phenomena  which  may  be 
produced  with  such  a  coil  I  have  here  selected  only  those 
which  appear  to  possess  some  features  of  novelty,  and  lead 
us  to  some  conclusions  of  interest.  One  will  not  find  it  at 
all  difficult  to  produce  in  the  laboratory,  by  means  of  b, 
many  other  phenomena  which  appeal  to  the  eye  even  more 
than  these  here  shown,  but  present  no  particular  feature  of 
novelty. 

Early  experimenteis  describe  the  display  of  spaiks  pro¬ 
duced  by  an  ordinary  large  induction  coil  upon  an  insulat¬ 
ing  plate  separating  the  terminals.  Quite  recently  Siemens 
performed  some  expeiiments  in  which  fine  effects  were  ob¬ 
tained,  which  were  seen  by  many  with  interest.  No  doubt 
large  coils,  even  if  operated  with  currents  of  low  frequen¬ 
cies,  are  capable  of  producing  beautiful  effects.  But  the 
largest  coil  ever  made  could  not,  by  far,  equal  the  magnifi¬ 
cent  display  of  streams  and  sparks  obtained  from  such  a 
disruptive  discharge  coil  when  properly  adjusted.  To  give 
an  idea,  a  coil  such  as  the  present  one  will  cover  easily  a 
plate  of  1  metre  in  diameter  completely  with  the  streams. 
The  best  way  to  perform  such  experiments  is  to  take  a  very 
thin  rubber  or  a  glass  plate  and  glue  on  one  side  of  it  a  nar¬ 
row  ring  of  tinfoil  of  very  large  diameter,  and  on  the  other 
a  circular  washer,  the  centre  of  the  latter  coinciding  with 
that  of  the  ring,  and  the  surfaces  of  both  being  preferably 


35 


equal,  so  as  to  keep  the  coil  well  balanced.  The  washer  and 
ring  should  be  connected  to  the  terminals  by  heavily  insu¬ 
lated  thin  wires.  It  is  easy  in  observing  the  effect  of  the 
capacity  to  produce  a  sheet  of  uniform  streams,  or  a  fine 
network  of  thin  silvery  threads,  or  a  mass  of  loud  brilliant 
sparks,  which  completely  cover  the  plate. 

Since  I  have  advanced  the  idea  of  the  conversion  by 
means  of  the  disruptive  discharge,  in  my  paper  before  the 
American  Institute  of  Electrical  Engineers  at  the  begin¬ 
ning  of  the  past  year,  the  interest  excited  in  it  has  been 
considerable.  It  affords  us  a  means  for  producing  any  po-  * 
tentials  by  the  aid  of  inexpensive  coils  operated  from  or¬ 
dinary  systems  of  distribution,  and — what  is  perhaps  more 
appreciated — it  enables  us  to  convert  currents  of  any  fre¬ 
quency  into  currents  of  any  other  lower  or  higher  fre¬ 
quency.  But  its  chief  value  will  perhaps  be  found  in  the 
help  which  it  will  afford  us  in  the  investigations  cf  the 
phenomena  of  phosphorescence,  which  a  disruptive  dis¬ 
charge  coil  is  capable  of  exciting  in  innumerable  cases 
where  ordinary  coils,  even  the  largest,  would  utterly  fail. 

Considering  its  probable  uses  for  many  practical  pur¬ 
poses,  and  its  possible  introduction  into  laboratories  for 
scientific  research,  a  few  additional  remarks  as  to  the  con¬ 
struction  of  such  a  coil  will  perhaps  not  be  found  super¬ 
fluous. 

It  is,  of  course,  absolutely  necessary  to  employ  in  such  a 
coil  wires  provided  with  the  best  insulation. 

Good  coils  may  be  produced  by  employing  wires  covered 
with  several  layers  of  cotton,  boiling  the  coil  a  long  time  in 
pure  wax,  and  coohng  under  moderate  pressure.  The  ad- 


vantage  of  such  a  coil  is  that  it  can  be  easily  handled,  but 
it  cannot  probably  give  as  satisfactory  results  as  a  coil  im¬ 
mersed  in  pure  oil.  Besides,  it  seems  that  the  presence  of 
a  large  body  of  wax  affects  the  coil  disadvantageous^, 
whereas  this  does  not  seem  to  be  the  case  with  oil.  Perhaps 
it  is  because  the  dielectric  losses  in  the  liquid  are  smaller. 

I  have  tried  at  first  silk  and  cotton  covered  wires  with 
oil  immersion,  but  I  have  been  gradually  led  to  use  gutta¬ 
percha  covered  wires,  which  proved  most  satisfactory. 
Gutta-percha  insulation  adds,  of  course,  to  the  capacity  of 
the  coil,  and  this,  especially  if  the  coil  be  large,  is  a  great 
disadvantage  when  extreme  frequencies  are  desired  ;  but, 
on  the  other  hand,  gutta-percha  will  withstand  much  m  ore 
than  an  equal  thickness  of  oil,  and  this  advan'age  should 
be  secured  at  any  price.  Once  the  coil  has  been  immersed, 
it  should  never  be  taken  out  of  the  oil  for  more  than  a  few 
hours,  else  the  gutta-percha  will  crack  up  and  the  coil  will 
not  be  worth  half  as  much  as  before.  Gut  a-percha  is  prob¬ 
ably  slowly  attacked  by  the  oil,  but  after  an  immersion  of 
eight  to  nine  months  I  have  found  no  ill  effects. 

I  have  obtained  in  commerce  two  kinds  of  gutta-percha 
wire:  in  one  the  insulation  sticks  tightly  to  the  metal,  in 
the  other  it  does  not.  Unless  a  special  method  is  followed 
to  expel  all  air,  it  is  much  safer  to  use  the  first  kind.  I 
wind  the  coil  within  an  oil  tank  so  that  all  interstices  are 
filled  up  with  the  oil.  Between  the  layers  I  use  cloth  boiled 
out  thoroughly  in  oil,  calculating  the  thickness  according 
to  the  difference  of  potential  between  the  turns.  There 
seems  not  to  be  a  very  great  difference  whatever  kind  of 
oil  is  used  ;  I  use  paraffine  or  linseed  oil. 


To  exclude  more  perfectly  the  air,  an  excellent  way  to 
proceed,  and  easily  practicable  with  small  coils,  is  the  fol¬ 
lowing  :  Construct  a  box  of  hard  wood  of  very  thick  boards 
which  have  been  for  a  long  time  boiled  in  oil.  The  boards 
should  be  so  joined  as  to  safely  withstand  the  external  air 
pressure.  The  coil  being  placed  and  fastened  in  position 
within  the  box,  the  latter  is  closed  with  a  strong  lid,  and 
covered  with  closely  fitting  metal  sheets,  the  joints  of  which 
are  soldered  very  carefully.  On  the  top  two  small  holes 
are  drilled,  passing  through  the  metal  sheet  anci  the  wood, 
and  in  these  holes  two  small  glass  tubes  are  inserted  and 
the  joints  made  air-tight.  One  of  the  tubes  is  connected  to 
a  vacuum  pump,  and  the  other  with  a  vessel  containing  a 
sufficient  quantity  of  boiled-out  oil.  The  latter  tube  has  a 
very  small  hole  at  the  bottom,  and  is  provided  with  a  stop¬ 
cock.  When  a  fairly  good  vacuum  has  been  obtained,  the 
stopcock  is  opened  and  the  oil  slowly  fed  in.  Proceeding 
in  this  manner,  it  is  impossible  that  any  big  bubbles,  which 
are  the  principal  danger,  should  remain  between  the  turns. 
The  air  is  most  completely  excluded,  probably  better  than 
by  boiling  out,  which,  however,  when  gutta-percha  coated 
wires  are  used,  is  not  practicable. 

For  the  primaries  I  use  ordinary  line  wire  with  a  thick 
cotton  coating.  Strands  of  very  thin  insulated  wires 
properly  interlaced  would,  of  course,  be  the  best  to 
employ  for  the  primaries,  but  they  are  not  to  be  had. 

In  an  experimental  coil  the  size  of  the  wires  is  not  of 
great  importance.  In  the  coil  here  used  the  primary  is  No. 
12  and  the  secondary  No.  24  Brown  &  Sharpe  gauge  wire  ; 
but  the  sections  may  be  varied  considerably.  It  would  only 


imply  different  adjustments  ;  the  results  aimed  at  would 
not  be  materially  affected. 

I  have  dwelt  at  some  length  upon  the  various  forms  of 
brush  discharge  became,  in  studying  them,  we  not  only  ob¬ 
serve  phenomena  which  please  our  eye,  but  also  afford  us 
food  for  thought,  and  lead  us  to  conclusions  of  practical 
importance.  In  the  use  of  alternating  currents  of  very  high 
tension,  too  much  precaution  cannot  be  taken  to  prevent 
the  brush  discharge.  In  a  main  conveying  such  currents, 
in  an  induction  coil  or  transformer,  or  in  a  condenser,  the 
brush  discharge  is  a  source  of  great  danger  to  the  insulation. 
In  a  condenser  especially  the  gaseous  matter  must  be  most 
carefully  expelled,  for  in  it  the  charged  surfaces  are  near 
each  other,  and  if  the  potentials  are  high,  just  as  sure  as  a 
weight  will  fall  if  let  go,  so  the  insulation  will  give  way  if  a 
single  gaseous  bubble  of  some  size  be  present,  whereas, 
if  all  gaseous  matter  were  carefully  excluded,  the 
condenser  would  safely  withstand  a  much  higher 
difference  of  potential.  A  main  conveying  alternating 
currents  of  very  high  tension  may  be  injured  merely  by  a 
blow  hole  or  small  crack  in  the  insulation,  the  more  so  as  a 
blowhole  is  apt  to  contain  gas  at  low  pressure;  and  as  it 
appears  almost  impossible  to  completely  obviate  such  little 
imperfections,  I  am  led  to  believe  that  in  our  future  distri¬ 
bution  of  electrical  energy  by  currents  of  very  high  ten¬ 
sion  liquid  insulation  will  be  used.  The  cost  is  a  great 
drawback,  but  if  we  employ  an  oil  as  an  insulator  the  dis¬ 
tribution  of  electrical  energy  with  something  like  100,000 
volts,  and  even  more,  become,  at  least  with  higher  frequen¬ 
cies,  so  easy  that  they  could  be  hardly  called  engineering 


(I . 

feats.  With  oil  insulation  and  alternate  current  motors 
transmissions  of  power  jcan_be  effpcted  with  safety  and 
upon  an  industrial  basis  at  distances  of  as  much  as  a  thou¬ 
sand  miles.  \\ 

A  peculiar  property  of  oils,  and  liquid  insulation  in  gen¬ 
eral,  when  subjected  to  rapidly  changing  electric  stresses, 
is  to  disperse  any  gaseous  bubbles  which  may  be  present, 
and  diffuse  them  through  its  mass,  generally  long  before 
any  injurious  break  can  occur.  This  feature  may  be  easily 
observed  with  an  ordinary  induction  coil  by  taking  the 
primary  out,  plugging  up  the  end  of  the  tube  upon  which 
the  secondary  is  wound,  and  filling  it  with  some  fairly 
transparent  insulator,  such  as  paraffine  oil.  A  primary  of 
a  diameter  something  like  six  millimetres  smaller  than  the 
inside  of  the  tube  may  be  inserted  in  the  oil.  When  the 
coil  is  set  to  work  one  may  see,  looking  from  the  top 
through  the  oil,  many  luminous  points — air  bubbles  which 
are  caught  by  inserting  the  primary,  and  which  are  ren¬ 
dered  luminous  in  consequence  of  the  violent  bombard¬ 
ment.  The  occluded  air,  by  its  impact  against  the  oil,  heats 
it ;  the  oil  begins  to  circulate,  carrying  some  of  the  air 
along  with  it,  until  the  bubbles  are  dispersed  and  the 
luminous  points  disappear.  In  this  manner,  unless  large 
bubbles  are  occluded  in  such  way  that  circulation  is  ren¬ 
dered  impossible,  a  damaging  break  is  averted,  the  only 
effect  being  a  moderate  warming  up  of  the  oil.  If,  instead 
of  the  liquid,  a  solid  insulation,  no  matter  how  thick,  were 
used,  a  breaking  through  and  injury  of  the  apparatus  would 
be  inevitable. 

The  exclusion  of  gaseous  matter  from  any  apparatus  in 


which  the  dielectric  is  subjected  to  more  or  less  rapidly 
changing  electric  forces  is,  however,  not  only  desirable  in 
order  to  avoid  a  possible  injury  of  the  apparatus,  but  also  on 
account  of  economy.  In  a  condenser,  for  instance,  as  long 
as  only  a  solid  or  only  a  liquid  dielectric  is  used,  the  loss  is 
small ;  but  if  a  gas  under  ordinary  or  small  pressure  be 
present  the  loss  may  be  very  great.  Whatever  the  nature 
of  the  force  acting  in  the  dielectric  may  be,  it  seems  that 
in  a  solid  or  liquid  the  molecular  displacement  produced  by 
the  force  is  small  :  hence  the  product  of  force  and  displace¬ 
ment  is  insignificant,  unless  the  force  be  very  great  ;  but 
in  a  gas  the  displacement,  and  therefore  this  product,  is 
considerable  ;  the  molecules  are  free  to  move,  they  reach 
high  speeds,  and  the  energy  of  their  impact  is  lost  in  heat 
or  otherwise.  If  the  gas  be  strongly  compressed,  the  dis¬ 
placement  due  to  the  force  is  made  smaller,  and  the  losses 
are  reduced. 

In  most  of  the  succeeding  experiments  I  prefer,  chiefly 
on  account  of  the  regular  and  positive  action,  to  employ 
the  alternator  before  referred  to.  This  is  one  of  the  sev¬ 
eral  machines  constructed  by  me  for  the  purposes  of  these 
investigations.  It  has  384  pole  projections,  and  is  capable 
of  giving  currents  of  a  frequency  of  about  10, COO  per  sec¬ 
ond.  This  machine  has  been  illustrated  and  briefly  de¬ 
scribed  in  my  first  paper  befoie  the  American  Institute  of 
Electrical  Engineers,  May  20, 1891,  to  which  I  have  already 
referred.  A  more  detailed  description,  sufficient  to  enable 
any  engineer  to  build  a  similar  machine,  will  be  found  in 
several  electrical  journals  of  that  period. 

The  induction  coils  operated  from  the  machine  are  rather 


41 


small,  containing  from  5,000  to  15,000  turns  in  the  second¬ 
ary.  They  are  immersed  in  boiled-out  linseed  oil,  con¬ 
tained  in  wooden  boxes  covered  with  zinc  sheet. 

I  have  found  it  advantageous  to  reverse  the  usual  posi¬ 
tion  of  the  wires,  and  to  wind,  in  these  coils,  the  primaries 
on  the  top;  this  allowing  the  use  of  a  much  bigger  primary, 
which,  of  course,  reduces  the  danger  of  overheating  and 
increases  the  output  of  the  coil.  I  make  the  primary  on 
each  side  at  least  one  centimetre  shorter  than  the  secondary , 
to  prevent  the  breaking  through  on  the  ends,  which  would 
surely  occur  unless  the  insulation  on  the  top  of  the  second¬ 
ary  be  very  thick,  and  this,  of  course,  would  be  disadvan¬ 
tageous. 

When  the  primary  is  made  movable,  which  is  necessary 
in  some  experiments,  and  many  times  convenient  for  the 
purposes  of  adjustment,  I  cover  the  secondary  with  wax, 
and  turn  it  off  in  a  lathe  to  a  diameter  slightly  smaller 
than  the  inside  of  the  primary  coil.  The  latter  I  provide 
with  a  handle  peaching  out  of  the  oil,  which  serves  to  shift 
it  in  any  pssition  along  the  secondary. 

I  will  now  venture  to  make,  in  regard  to  the  general 
manipulation  of  induction  coils,  a  few  observations  bear¬ 
ing  upon  points  which  have  not  been  fully  appreciated  in 
earlier  experiments  with  such  coils,  and  are  even  now  often 
overlooked. 

The  secondary  of  the  coil  possesses  usually  such  a  high 
self-induction  that  the  current  through  the  wire  is  inap¬ 
preciable,  and  may  be  so  even  when  the  terminals  are 
joined  by  a  conductor  of  small  resistance,  If  capacity  is 
aided  to  the  terminals,  the  self-induction  is  counteracted, 


42 


and  a  stronger  current  is  made  to  flow  through  the  second¬ 
ary,  though  its  terminals  are  insulated  from  each  other. 
To  one  entirely  unacquainted  with  the  properties  of  alter¬ 
nating  currents  nothing  will  look  more  puzzling.  This 
feature  was  illustrated  in  the  experiment  performed  at  the 
beginning  with  the  top  plates  of  wire  gauze  attached  to  the 
terminals  and  the  rubber  plate.  When  the  plates  of  wire 
gauze  were  close  together,  and  a  small  arc  passed  between 
them,  the  arc  pi  evented  a  strong  current  from  passing 
through  the  secondary,  because  it  did  away  with  the  capacity 
on  the  terminals;  when  the  rubber  plate  was  inserted  be¬ 
tween,  the  capacity  of  the  condenser  formed  counteracted 
the  self-induction  of  the  secondary,  a  stronger  current 
passed  now,  the  coil  performed  more  work,  and  the  dis¬ 
charge  was  by  far  more  powerful. 

The  first  thing,  then,  in  operating  the  induction  coil  is  to 
combine  capacity  with  the  secondary  to  overcome  the 
self-induction.  If  the  frequencies  and  potentials  are  very 
high  gaseous  matter  should  be  carefully  kept  away  from 
the  charged  surfaces.  If  Leyden  jars  are  used,  they  should 
be  immersed  in  oil,  as  otherwise  considerable  dissipation 
may  occur  if  the  jars  are  greatly  strained.  When  high 
frequencies  are  used,  it  is  of  equal  importance  to  combine 
a  condenser  with  the  primary.  One  may  use  a  condenser 
connected  to  the  ends-of  the  primary  or  to  the  terminals  of 
the  alternator,  but  the  latter  is  not  to  be  recommended,  as 
the  machine  might  be  injured.  The  best  way  is  undoubt¬ 
edly  to  use  the  condenser  in  series  with  the  primary  and 
with  the  alternator,  and  to  adjust  its  capacity  so  as  to  an¬ 
nul  the  self-induction  of  both  the  latter.  The  condenser 


43 


should  be  adjustable  by  very  small  steps,  and  for  a  finer 
adjustment  a  small  oil  condenser  with  movable  plates  may 
be  used  conveniently. 

I  think  it  best  at  this  juncture  to  bring  before  you  a  phe¬ 
nomenon,  observed  by  me  some  time  ago,  which  to  the 
purely  scientific  investigator  may  perhaps  appear  more  in¬ 
teresting  than  any  of  the  results  which  I  have  the  privilege 
to  present  to  you  this  evening. 

It  may  be  quite  properly  ranked  among  the  brush  phe¬ 
nomena — in  fact,  it  is  a  brush,  formed  at,  or  near,  a  single 
terminal  in  high  vacuum. 

In  bulbs  provided  with  a  conducting  terminal,  though  it 
be  of  aluminium,  the  brush  has  but  an  ephemeral  existence, 
and  cannot,  unfortunately,  be  indefinitely  preserved  in  its 
most  sensitive  state,  even  in  a  bulb  devoid  of  any  conduct¬ 
ing  electrode.  In  studying  the  phenomenon,  by  all  means 
a  bulb  having  no  leading-in  wire  should  be  used.  I  have 
found  it  best  to  use  bulbs  constructed  as  indicated  in  Figs. 
12  and  13. 

In  Fig.  12  the  bulb  comprises  an  incandescent  lamp  globe 
L,  in  the  neck  of  which  is  sealed  a  barometer  tube  b,  the 
end  of  which  is  blown  out  to  form  a  small  sphere  s.  This 
sphere  should  be  sealed  as  closely  as  possible  in  the  centre 
of  the  large  globe.  Before  sealing,  a  thin  tube  t,  of  alu¬ 
minium  sheet,  may  be  slipped  in  the  barometer  tube,  but  it 
is  not  important  to  employ  it. 

The  small  hollow  sphere  s  is  filled  with  some  conducting 
powder,  and  a  wire  w  is  cemented  in  the  neck  for  the  pur¬ 
pose  of  connecting  the  conducting  powder  with  the  gen¬ 
erator, 


44 


The  construction  shown  in  Fig.  13  was  chosen  in  order  to 
remove  from  the  brush  any  conducting  body  which  might 
possibly  affect  it.  The  bulb  consists  in  this  case  of  a  lamp 
globe  L,  which  has  a  neck  n,  provided  with  a  tube  band 


Bulbs  for  Producing  Rotating  Brush. 


small  sphere  s,  sealed  to  it,  so  that  two  entirely  independ¬ 
ent  compartments  are  formed,  as  indicated  in  the  drawing. 
When  the  bulb  is  in  use,  the  neck  n  is  provided  with  a  tin- 
foil  coating,  which  is  connected  to  the  generator  and  acts 


45 


inductively. upon  the  moderately  rarefied  and  highly  con¬ 
ducting  gas  inclosed  in  the  neck.  From  there  the  current 
passes  through  the  tube  b  into  the  small  sphere  s,  to  act  by 
induction  upon  the  gas  contained  in  the  globe  L. 

It  is  of  advantage  to  make  the  tube  t  very  thick,  the  hole 
through  it  very  small,  and  to  blow  the  sphere  s  very  tliin. 
It  is  of  the  greatest  importance  that  the  sphere  s  be  placed 
in  the  centre  of  the  globe  L. 


Fig.  14.— Forms  and  Phases  of  the  Rotating  Brush. 

Figs.  14,  15  and  16  indicate  different  forms,  or  stages,  of 
the  brush.  Fig.  14  shows  the  brush  as  it  first  appears  in  a 
bulb  provided  with  a  conducting  terminal ;  but,  as  in  such 
a  bulb  it  very  soon  disappears — often  after  a  few  minutes — I 
will  confine  myself  to  the  description  of  the  phenomenon 
as  seen  in  a  bulb  without  conducting  electrode.  It  is  ob¬ 
served  under  the  following  conditions  : 

When  the  globe  L  (Figs.  12  and  13)  is  exhausted  to  a 


46 


very  high  degree,  generally  the  bulb  is  not  excited  upon 
connecting  the  wire  w  (Fig.  12)  or  the  tinfoil  coating  of  the 
bulb  (Fig.  13)  to  the  terminal  of  the  induction  coil.  To  ex¬ 
cite  it,  it  is  usually  sufficient  to  grasp  the  globe  L  with  the 


hand.  An  intense  phosphorescence  then  spreads  at  first 
over  the  globe,  but  soon  gives  place  to  a  white,  misty  light. 
Shortly  afterward  one  may  notice  that  the  luminosity  is  un¬ 
evenly  distributed  in  the  globe,  and  after  passing  the  cur- 


47 


rent  for  some  time  the  bulb  appears  as  in  Fig.  15.  From 
this  stage  the  phenomenon  will  gradually  pass  to  that  in¬ 
dicated  in  Fig.  16,  after  some  minutes,  hours,  days  or 
weeks,  according  as  the  bulb  is  worked.  Warming  the 
bulb  or  increasing  the  potential  hastens  the  transit. 

When  the  brush  assumes  the  form  indicated  in  Fig.  16, 
it  may  be  brought  to  a  state  of  extreme  sensitiveness  to 
electrostatic  and  magnetic  influence.  The  bulb  hanging 
straight  down  from  a  wire,  and  all  objects  being  remote 
from  it,  the  approach  of  the  observer  at  a  few  paces  from 
the  bulb  will  cause  the  brush  to  fly  to  th  opposite  side, 
and  if  he  walks  around  the  bulb  it  will  always  keep  on  the 
opposite  side.  It  may  begin  to  spin  around  the  terminal 
long  before  it  reaches  that  sensitive  stage.  When  it  begins 
to  turn  around  principally,  but  aho  before,  it  is  affected  by 
a  magnet,  and  at  a  certain  stage  it  is  susceptible  to  mag¬ 
netic  influence  to  an  astonishing  degree.  A  small  perma¬ 
nent  magnet,  with  its  poles  at  a  distance  of  no  more  than 
two  centimetres,  will  affect  it  visibly  at  a  distance  of  two 
metres,  slowing  down  or  accelerating  the  rotation  accord¬ 
ing  to  how  it  is  held  relatively  to  the  brush.  I  think  I 
have  observed  that  at  the  stage  when  it  is  most  sensitive  to 
magnetic,  it  is  not  most  sensitive  to  electrostatic,  influence. 
My  explanation  is,  that  the  electrostatic  attraction  between 
the  brush  and  the  glass  of  the  bulb,  which  retards  the  rota¬ 
tion,  grows  much  quicker  than  the  magnetic  influence 
when  the  intensity  of  the  stream  is  increased. 

When  the  bulb  hangs  with  the  globe  L  down,  the  rota¬ 
tion  is  always  clockwise.  In  the  southern  hemisphere  it 
would  occur  in  the  opposite  direction  and  on  the  equator 


48 


the  brush  should  not  turn  at  all.  1  he  rotation  may  be  re¬ 
versed  by  a  magnet  kept  at  some  distance.  The  brush  ro¬ 
tates  best,  seemingly,  when  it  is  at  right  angles  to  the  lines 
of  force  of  the  earth.  It  very  likely  rotates,  when  at  its 
maximum  speed,  in  synchronism  with  the  alternations,  say 
10,000  times  a  second.  The  rotation  can  be  slowed  down  or 
accelerated  by  the  approach  or  receding  of  the  observer,  or 
any  conducting  body,  but  it  cannot  be  reversed  by  putting 
the  bulb  in  any  position.  When  it  is  in  the  state  of  the 
highest  sensitiveness  and  the  potential  or  frequency  be 
varied  the  sensitiveness  is  rapidly  diminished.  Chang¬ 
ing  either  of  these  but  little  will  generally  stop  the  rotation. 
% 

The  sensitiveness  is  likewise  affected  by  the  variations  of 
temperature.  To  attain  great  sensitiveness  it  is  necessary 
to  have  the  small  sphere  s  in  the  centre  of  the  globe  L,  as 
otherwise  the  electrostatic  action  of  the  glass  of  the  globe 
will  tend  to  stop  the  rotation.  The  sphere  s  should  be 
small  and  of  uniform  thickness  ;  any  dissymmetry  of  course 
has  the  effect  to  diminish  the  sensitiveness. 

The  fact  that  the  brush  rotates  in  a  definite  direction  in 
a  permanent  magnetic  field  seems  to  show  that  in  alternat¬ 
ing  currents  of  very  high  frequency  the  positive  and  nega¬ 
tive  impulses  are  not  equal,  but  that  one  always  preponder¬ 
ates  over  the  other. 

Of  course,  this  rotation  in  one  direction  may  be  due  to 
the  action  of  two  elements  of  the  same  current  upon  each 
other,  or  to  the  action  of  the  field  produced  by  one  of  the 
elements  upon  the  other,  as  iu  a  series  motor,  without  nec¬ 
essarily  one  impulse  being  stronger  than  the  other.  The 
fact  that  the  brush  turns,  as  far  as  I  could  observe,  in  any 


49 


position,  would  speak  for  this  view.  In  such  case  it  would 
turn  at  any  point  of  the  earth’s  surface.  But,  on  the  other 
hand ,  it  is  then  hard  to  explain  why  a  permanent  magnet 
should  reverse  the  rotation,  and  one  must  assume  the  pre¬ 
ponderance  of  impulses  of  one  kind. 

As  to  the  causes  of  the  formation  of  the  brush  or  stream, 
I  thinx  it  is  due  to  the  electrostatic  action  of  the  globe  and 
the  dissymmetry  of  the  parts.  If  the  small  bulb  s  and  the 
globe  L  were  perfect  concentric  spheres,  and  the  glass 
throughout  of  the  same  thickness  and  quality,  I  think  the 
brush  would  not  form,  as  the  tendency  to  pass  would  be 
equal  on  all  sides.  That  the  formation  of  the  stream  is  due 
to  an  irregularity  is  apparent  from  the  fact  that  it  has  the 
tendency  to  remain  in  one  position,  and  rotation  occurs 
most  generally  only  when  it  is  brought  out  of  this  position 
by  electrostatic  or  magnetic  influence.  When  in  an  ex¬ 
tremely  sensitive  state  it  rests  in  one  position,  most  curious 
experiments  may  be  performed  with  it.  For  instance,  the 
experimenter  may,  by  selecting  a  proper  position,  approach 
the  hand  at  a  certain  considerable  distance  to  the  bulb,  and 
he  may  cause  the  brush  to  pass  off  by  merely  stiffening  the 
muscles  of  the  arm.  When  it  begins  to  rotate  slowly,  and 
the  hands  are  held  at  a  proper  distance,  it  is  impossible  to 
make  even  the  slightest  motion  without  producing  a  visible 
effect  upon  the  brush.  A  metal  plate  connected  to  the  other 
terminal  of  the  coil  affects  it  at  a  great  distance,  slowing 
down  the  rotation  often  to  one  turn  a  second. 

I  am  firmly  convinced  that  such  a  brush,  when  we  learn 
how  to  produce  it  properly,  will  prove  a  valuable  aid  in  the 
investigation  of  the  nature  of  the  forces  acting  in  an  elec- 


50 


trostatic  or  magnetic  field.  If  there  is  any  motion  which 
is  measurable  going  on  in  the  space,  such  a  brush  ought  to 
reveal  it.  It  is,  so  to  speak,  a  beam  of  light,  frictionless, 
devoid  of  inertia. 

I  think  that  it  may  find  practical  applications  in  telegra¬ 
phy.  With  such  a  brush  it  would  be  possible  to  send 
dispatches  across  the  Atlantic,  for  instance,  with  any  speed, 
sin<  e  its  sensitiveness  may  be  so  great  that  the  slightest 
changes  will  affect  it.  If  it  were  possible  to  make  the 
stream  more  intense  and  very  narrow,  its  deflections  could 
be  easily  photographed. 

I  have  been  interested  to  find  whether  there  is  a  rotation 
of  the  stream  itself,  or  whether  there  is  simply  a  stress 
traveling  around  in  the  bulb.  For  this  purpose  I  mounted 
a  light  mica  fan  so  that  its  vanes  were  in  the  path  of  the 
brush.  If  the  stream  itself  was  rotating  the  fan  would  be 
spun  around.  I  could  produce  no  distinct  rotation  of  the 
fan,  although  I  tried  the  experiment  repeatedly;  but  as  the 
fan  exerted  a  noticeable  influence  on  the  stream,  and  the 
apparent  rotation  of  the  latter  was,  in  this  case,  never  quite 
satisfactory,  the  experiment  did  not  appear  to  be  conclusive. 

I  have  been  unable  to  produce  the  phenomenon  with  the 
disruptive  discharge  coil,  although  every  other  of  these 
phenomena  can  be  well  produced  by  it — many,  in  fact, 
much  better  than  with  coils  operated  from  an  alternator. 

It  may  be  possible  to  produce  the  brush  by  impulses  of 
one  direction,  or  even  by  a  steady  potential,  in  which  case 
it  would  be  still  more  sensitive  to  magnetic  influence. 

In  operating  an  induction  coil  with  rapidly  alternating 
currents,  wre  realize  with  astonishment,  for  the  first  time, 


51 


the  great  importance  of  the  relation  of  capacity,  self-in¬ 
duction  and  frequency  as  regards  the  general  result.  The 
effects  of  capacity  are  the  most  striking,  for  in  these  exper¬ 
iments,  since  the  self-induction  and  frequency  both  are 
high,  the  critical  capacity  is  very  small,  and  need  be  but 
slightly  varied  to  produce  a  very  considerable  change.  The 
experimenter  may  bring  his  body  in  contact  with  the  ter¬ 
minals  of  the  secondary  of  the  coil,  or  attach  to  one  or  both 
terminals  insulated  bodies  of  very  small  bulk,  such  as  bulbs, 
and  he  may  produce  a  considerable  rise  or  fall  of  potential, 
and  greatly  affect  the  flow  of  the  current  through  the  pri¬ 
mary.  In  the  experiment  before  shown,  in  which  a  brush 
appears  at  a  wire  attached  to  one  terminal,  and  the  wire  is 
vibrated  when  the  experimenter  brings  his  insulated  body 
in  contact  with  the  other  terminal  of  the  coil,  the  sudden 
rise  of  potential  was  made  evident. 

I  may  show  you  the  behavior  of  the  coil  in  another  man¬ 
ner  which  possesses  a  feature  of  some  interest.  I  have  here 
a  little  light  fan  of  aluminium  sheet,  fastened  to  a  needle 
and  arranged  to  rotate  freely  in  a  metal  piece  screwed  to 
one  of  the  terminals  of  the  coil.  When  the  coil  is  set  to 
work,  the  molecules  of  the  air  are  rhythmically  attracted 
and  repelled.  As  the  force  with  which  they  are  repelled  is 
greater  than  that  with  which  they  are  attracted,  it  results 
that  there  is  a  repulsion  exerted  on  the  surfaces  of  the  fan. 
If  the  fan  were  made  simply  of  a  metal  sheet,  the  repulsion 
would  be  equal  on  the  opposite  sides,  and  would  produce  no 
effect.  But  if  one  of  the  opposing  surfaces  is  screened,  or 
if,  generally  speaking,  the  bombardment  on  this  side  is 
weakened  in  some  way  or  other,  there  remains  the  repul- 


sion  exerted  upon  the  other,  and  the  fan  is  set  in  rotation . 
The  screening  is  best  effected  by  fastening  upon  one  of  the  op¬ 
posing  sides  of  the  fan  insulated  conducting  coatings,  or,  if 
the  fan  is  made  in  the  shape  of  an  ordinary  propeller  screw, 
by  fastening  on  one  side,  and  close  to  it,  an  insulated  metal 
plate.  The  static  screen  may,  however,  be  omitted,  and 
simply  a  thickness  of  insulating  material  fastened  to  one  of 
the  sides  of  the  fan. 

To  show  the  behavior  of  the  coil,  the  fan  may  be  placed 
upon  the  terminal  and  it  will  readily  rotate  when  the  coil 
is  operated  by  currents  of  very  high  frequency.  With  a 
steady  potential,  of  course,  and  even  with  alternating  cur¬ 
rents  of  very  low  frequency,  it  would  not  turn,  because  of 
the  very  slow  exchange  of  air  and,  consequently,  smaller 
bombardment;  but  in  the  latter  case  it  might  turn  if  the 
potential  were  excessive.  With  a  pin  wheel,  quite  the  op¬ 
posite  rule  holds  good  ;  it  rotates  best  with  a  steady  poten¬ 
tial,  and  the  effort  is  the  smaller  the  higher  the  frequency. 
Now,  it  is  very  easy  to  adjust  the  conditions  so  that  the 
potential  is  normally  not  sufficient  to  turn  the  fan,  but 
that  by  connecting  the  other  terminal  of  the  coil  with  an 
insulated  body  it  rises  to  a  much  greater  value,  so  as  to 
rotate  the  fan,  and  it  is  likewise  possible  to  stop  the  rota¬ 
tion  by  connecting  to  the  terminal  a  body  of  different 
size,  thereby  diminishing  the  potential. 

Instead  of  using  the  fan  in  this  experiment,  we  may  use 

the  “electric”  radiometer  with  similar  effect.  But  in  this 

« 

case  it  will  be  found  that  the  vanes  will  rotate  only  at  high 
exhaustion  or  at  ordinary  pressures;  they  will  not  rotate  at 
moderate  pressures,  when  the  air  is  highly  conducting. 


M 

Tins  curious  observation  was  made  conjointly  by  Professor 
Crookes  and  myself.  I  attribute  tlie  result  to  the  high  con¬ 
ductivity  of  the  air,  the  molecules  of  which  then  do  not 
act  as  independent  carriers  of  electric  charges,  but  act  all 
together  as  a  single  conducting  body.  In  such  case,  of 
course,  if  there  is  any  repulsion  at  all  of  the  molecules 
from  the  vanes,  it  must  be  very  small.  It  is  possible,  how¬ 
ever,  that  the  result  is  in  part  due  to  the  fact  that  the 
greater  part  of  the  discharge  passes  from  the  leading-in 
wire  through  die  highly  conducting  gas,  instead  of  pass¬ 
ing  off  from  the  conducting  vanes. 

In  trying  the  preceding  experiment  widi  the  electric 
radiometer  the  potential  should  not  exceed  a  certain  limit, 
as  then  the  electrostatic  attraction  between  the  vanes  and 
the  glass  of  the  bulb  may  be  so  great  as  to  stop  the  rota- 
tation. 

.  '  \ 

A  most  curious  feature  of  alternate  currents  of  high  fre¬ 
quencies  and  potentials  is  that  they  enable  us  to  perform 
many  experiments  by  the  use  of  one  wire  only.  In  many 
respects  this  feature  is  of  great  interest. 

In  a  type  cf  alternate  current  motor  invented  by  me  some 
years  ago  I  produced  rotation  by  inducing,  by  means  of  a 
single  alternating  current  passed  through  a  motor  circuit, 
in  the  mass  or  other  circuits  of  the  motor,  secondary  cur¬ 
rents,  which,  jointly  with  the  primary  or  inducing  current, 
created  a  moving  field  of  force.  A  simple  but  crude  form 
of  such  a  motor  is  obtained  by  winding  upon  an  iron  core  a 
primary,  and  close  to  it  a  secondary  coil,  joining  the  ends 
of  the  latter  and  placing  a  freely  movabA  metal  disc 
within  the  influence  of  the  field  produced  by  both.  The 


54 


iron  core  is  employed  for  obvious  reasons,  but  it  is  not  es¬ 
sential  to  the  operation.  To  improve  the  motor,  the  iron 
core  is  made  to  encircle  the  armature.  Again  to  improve, 
the  secondary  coil  is  made  to  overlap  partly  the  primary,  so 
that  it  cannot  free  itself  from  a  strong  inductive  action  of 
the  latter,  repel  its  lines  as  it  may.  Once  more  to  im¬ 
prove,  the  proper  difference  of  phase  is  obtained  between 
the  primary  and  secondary  currents  by  a  condenser,  self- 
induction  ^resistance  or  equivalent  windings. 

I  had  discovered,  however,  that  rotation  is  produced  by 
means  of  a  single  coil  and  core ;  my  explanation  of  the 
phenomenon,  and  leading  thought  in  trying  the  experi¬ 
ment,  being  that  there  must  be  a  true  time  lag  in  the  mag¬ 
netization  of  the  core.  I  remember  the  pleasure  I  had  when, 
in  the  writings  of  Professor  Ayrton,  which  came  later  to 
iny  hand,  I  found  the  idea  of  the  time  lag  advocated. 
Whether  there  is  a  true  time  lag,  or  whether  the  retarda¬ 
tion  is  due  to  eddy  currents  circulating  in  minute  paths, 
must  remain  an  open  question,  but  the  fact  is  that  a  coil 
wound  upon  an  iron  core  and  traversed  by  an  alternating 
current  creates  a  moving  field  of  force,  capable  of  setting 
an  armature  in  rotation.  It  is  of  some  interest,  in  conjunc¬ 
tion  with  the  historical  Arago  experiment,  to  mention  that 
in  lag  or  phase  motors  I  have  produced  rotation  in  the  oppo¬ 
site  direction  to  the  moving  field,  which  means  that  in  that 
experiment  the  magnet  may  not  rotate,  or  may  even  rotate 
in  the  opposite  direction  to  the  moving  disc.  Here,  then,  is 
a  motor  (diagrammatically  illustrated  in  Fig.  17),  compris¬ 
ing  a  coil  and  iron  core,  and  a  freely  movable  copper 
disc  in  proximity  to  the  latter. 


55 


To  demonstrate  a  novel  and  interesting  feature,  I  have, 

for  a  reason  which  I  will  explain,  selected  this  type  of 

» 

motor.  When  the  ends  of  the  coil  are  connected  to  the 
terminals  of  an  alternator  the  disc  is  set  in  rotation.  But 
it  is  not  this  experiment,  now  well  known,  which  I  desire 


to  perform.  What  I  wish  to  show  you  is  that  this  motor 
rotates  with  one  single  connection  between  it  and  the  gen¬ 
erator;  that  is  to  say,  one  terminal  of  the  motor  is  connected 
to  one  terminal  of  the  generator — in  this  case  the  secondary 
of  a  high-tension  induction  coil — the  other  terminals  of 


56 


motor  and  generator  being  insulated  in  space.  To  produce 
rotation  it  is  generally  (but  not  absolutely)  necessary  to 
connect  the  free  end  of  the  motor  coif  to  an  insulated  body 
of  some  size.  The  experimenter’s  body  is  more  than  suffi¬ 
cient.  If  he  touches  the  free  terminal  with  an  object 
held  in  the  hand,  a  current  passes  through  the 
coil  and  the  copper  disc  is  set  in  rotation.  If  an 
exhausted  tube  is  put  in  series  with  the  coil,  the  tube 
lights  brilliantly,  showing  the  passage  of  a  strong  cur¬ 
rent.  Instead  of  the  experimenter’s  body,  a  small 
metal  sheet  suspended  on  a  cord  may  be  used  with  the 
same  result.  In  this  case  the  plate  acts  as  a  condenser  in 
series  with  the  coil.  It  counteracts  the  self-induction  of 
the  latter  and  allows  a  strong  current  to  pass.  In  such  *' 
combination,  the  greater  the  self-induction  of  the  coil  the 
smaller  need  be  the  plate,  and  this  means  that  a  lower  fre¬ 
quency,  or  eventually  a  lower  potential,  is  required  to 
operate  the  motor.  A  single  coil  wound  upon  a  core  has  a 
high  self-induction;  for  this  reason  principally,  this  type  of 
motor  was  chosen  to  perform  the  experiment.  Were  a  sec¬ 
ondary  closed  coil  wound  upon  the  core,  it  would  tend  to 
diminish  the  self-induction,  and  then  it  would  be  necessary 
to  employ  a  much  higher  frequency  and  potential.  Neither 
would  be  advisable,  for  a  higher  potential  would  endanger 
the  insulation  of  the  small  primary  coil,  and  a  higher  fre¬ 
quency  would  result  in  a  materially  diminished  torque. 

It  should  be  remarked  that  when  such  a  motor  with  a  . 
closed  secondary  is  used,  it  is  not  at  all  easy  to  obtain  rota¬ 
tion  with  excessive  frequencies,  as  the  secondary  cuts  off 
almost  completely  the  lines  of  the  primary — and  this,  of 


57 


course,  the  more,  the  higher  the  frequency — and  allows  the 
passage  of  but  a  minute  current.  In  such  a  case,  unless  the 
secondary  is  closed  through  a  condenser,  it  is  almost  essen¬ 
tial,  in  order  to  produce  rotation,  to  make  the  primary  and 
secondary  coils  overlap  each  other  more  or  less. 

But  there  is  an  additional  feature  of  interest  about  this 
motor,  namely,  it  is,  not  necessary  to  have  even  a  single 
connection  between  the  motor  and  generator,  except,  per¬ 
haps,  through  the  ground;  for  not  only  is  an  insulated  plate 
capable  of  giving  off  energy  into  space,  but  it  is  likewise 
capable  of  deriving  it  from  an  alternating  electrostatic 
field,  though  in  the  latter  case  the  available  energy  is  much 
smaller.  In  this  instance  one  of  the  motor  terminals  is  con¬ 
nected  to  the  insulated  plate  or  body  located  within  the  al¬ 
ternating  electrostatic  field,  and  the  other  terminal  prefer¬ 
ably  to  the  ground. 

It  is  quite  possible,  however,  that  such  “no-wire”  motors, 
as  they  might  be  called,  could  be  operated  by  conduction 
through  the  rarefied  air  at  considerable  distances.  Alter¬ 
nate  currents,  especially  of  high  frequencies,  pass  with  as¬ 
tonishing  freedom  through  even  sligh  tly  rarefied  gases. 
The  upper  strata  of  the  air  are  rarefied.  To  reach  a  number 
of  miles  out  into  space  requires  the  overcoming  of  difficul¬ 
ties  of  a  merely  mechanical  nature.  There  is  no  doubt  that 
with  the  enormous  potentials  obtainable  by  the  use  of  high 
frequencies  and  oil  insulation  luminous  discharges  might 
be  passed  through  many  miles  of  rarefied  air,  and  that,  by 
thus  directing  the  energy  of  many  hundreds  or  thousands 
of  liorse-power,  motors  or  lamps  might  be  operated  at  con¬ 
siderable  distances  from  stationary  sources.  But  such 


J  *  k 


58 

schemes  are  mentioned  merely  as  possibilities.  We  shall 
have  no  need  to  transmit  power  in  tliis  way.  We  shall 
have  ncTneetl'  to  tfrOTlSwwTpower  at  all.  Ere  many  genera¬ 
tions  pass,  our  machinery  will  be  driven  by  a  power  ob¬ 
tainable  at  any  point  of  the^.  iiniverse.  This  idea  is 
not  novel.  Men  have  been  led  to  it  long  ago  by  instinct 
or  reason.  It  has  been  expressed  in  many  ways,  and  in 
many  places,  in  the  history  of  old  and  new.  We  find  it  in 
the  delightful  myth  of  Antheus,  who  derives  power 
from  the  earth;  we  find  it  among  the  subtile  speculations 
of  one  of  your  splendid  mathematicians,  and  in  many 
hints  and  statements  of  thinkers  of  the  present  time. 
Throughout  space  there  is  energy.  Is  this  energy  static 
or  kinetic?  If  static  our  hopes  are  in  vain;  if  kinetic- 
-and  this  we  know  it  is,  for  certain — then  it  is  a  mere  ques¬ 
tion  of  time  when  men  will  succeed  in  attaching  their 
machinery  to  the  very  wheelwork  of  nature.  Of  all,  liv¬ 
ing  or  dead,  Crookes  came  nearest  to  doing  it.  His  radi¬ 
ometer  will  turn  in  the  light  of  day  and  in  the  darkness 
of  the  night;  it  will  turn  everywhere  where  there  is  heat, 
and  heat  is  everywhere.  But,  unfortunately,  this  beauti¬ 
ful  little  machine,  while  it  goes  down  to  posterity  as  the 
most  interesting,  must  likewise  be  put  on  record  as  the 
most  inefficient  machine  ever  invented  ! 

The  preceding  experiment  is  only  one  of  many  equally 
interesting  experiments  which  may  be  performed  by  the 
use  of  only  one  wire  with  alternate  currents  of  high  poten¬ 
tial  and  frequency.  We  may  connect  an  insulated  line  to 
a  source  of  such  currents,  we  may  pass  an  inappreciable 
current  over  the  line,  and  on  any  point  of  the  same  we  are 


59 


able  to  obtain  a  heavy  current,  capable  of  fusing  a  thick 
copper  wire.  Or  we  may,  by  the  help  of  some  artifice,  de¬ 
compose  a  solution  in  any  electrolytic  cell  by  connecting 
only  one  pole  of  the  cell  to  the  line  or  source  of  energy.  Or 
we  may,  by  attaching  to  the  line,  or  only  bringing  into  its 
vicinity,  light  up  an  incandescent  lamp,  an  exhausted  tube, 
or  a  phosphorescent  bulb. 

However  impracticable  this  plan  of  working  may  appear 
in  many  cases,  it  certainly  seems  practicable,  and  even 
recommendable,  in  the  production  of  light.  A  perfected 
lamp  would^  require  but  little  energy,  and  if  wires  were 
used  at  all  we  ought  to  be  able  to  supply  tbat  energy  with- 
out  a  return  wire. 

It  is  now  a  fact  that  a  body  may  be  rendered  incandes¬ 
cent  or  phosphorescent  by  bringing  it  either  in  single  con¬ 
tact  or  merely  in  the  vicinity  of  a  source  of  electric  im¬ 
pulses  of  the  proper  character,  and  that  in  this  manner  a 
quantity  of  light  sufficient  to  afford  a  practical  illuminant 
may  be  produced.  It  is,  therefore,  to  say  the  least,  worth 
while  to  attempt  to  determine  the  best  conditions  and  to 
invent  the  best  appliances  for  attaining  this  object. 

Some  experiences  have  already  been  gained  in  this  direc¬ 
tion,  and  I  will  dwell  on  them  briefly,  in  the  hope  that  they 
might  prove  useful. 

The  heating  of  a  conducting  body  inclosed  in  a  bulb,  and 
connected  to  a  source  of  rapidly  alternating  electric  im¬ 
pulses,  is  dependent  on  so  many  things  of  a  different  nature, 
that  it  would  be  difficult  to  give  a  generally  applicable 
rule  under  wThich  the  maximum  heating  occurs.  As  re¬ 
gards  the  size  of  the  vessel,  I  have  lately  found  that  at  or- 


60 


dinary  or  only  slightly  differing  atmospheric  pressures, 
when  air  is  a  good  insulator,  and  hence  practically  the 
same  amount  of  energy  by  a  certain  potential  and  fre¬ 
quency  is  given  off  from  the  body,  whether  the  bulb  be 
small  or  large,  the  body  is  brought  to  a  higher  temperature 
if  inclosed  in  a  small  bulb,  because  of  the  better  confine¬ 
ment  of  heat  in  this  case. 

At  lower  pressures,  when  air  becomes  more  or  less  con¬ 
ducting,  or  if  the  air  be  sufficiently  warmed  as  to  become 
conducting,  the  body  is  rendered  more  intensely  incandes¬ 
cent  in  a  large  bulb,  obviously  because,  under  otherwise 
equal  conditions  of  test,  more  energy  may  be  given  off  from 
the  body  when  the  bulb  is  large. 

At  very  high  degrees  of  exhaustion,  when  the  matter  in 
the  bulb  becomes  “radiant,”  a  large  bulb  has  still  an  ad¬ 
vantage,  but  a  comparatively  slight  one,  over  the  small 
bulb. 

Finally,  at  excessively  high  degrees  of  exhaustion,  which 
cannot  be  reached  except  by  the  employment  of  special 
means,  there  seems  to  be,  beyond  a  certain  and  rather 
small  size  of  vessel,  no  perceptible  difference  in  the  heating. 

These  observations  were  the  result  of  a  number  of  ex¬ 
periments,  of  which  one,  showing  the  effect  of  the  size  of 
the  bulb  at  a  high  degree  of  exhaustion,  may  be  described 
and  shown  here,  as  it  presents  a  feature  of  interest.  Three 
spherical  bulbs  of  2  inches,  3  inches  and  4  inches  diameter 
were  taken,  and  in  the  centre  of  each  was  mounted  an 
equal  length  of  an  ordinary  incandescent  lamp  filament  of 
uniform  thickness.  In  each  bulb  the  piece  of  filament 
was  fastened  to  the  leading-in  wire  of  platinum,  con- 


61 


tained  in  a  glass  stem  sealed  in  the  bulb  ;  care  being 
taken,  of  course,  to  make  everything  as  nearly  alike 
as  possible.  On  each  glass  stem  in  the  inside  of  the 
bulb  was  slipped  a  highly  polished  tube  made  of 
aluminium  sheet,  which  litted  the  stem  and  was 
held  on  it  by  spring  pressure.  The  function  of  this 
aluminium  tube  will  be  explained  subsequently.  In 
each  bulb  an  equal  length  of  filament  protruded  above 
the  metal  tube.  It  is  sufficient  to  say  now  that  under  these 
conditions  equal  lengths  of  filament  of  the  same  thick¬ 
ness — in  other  words,  bodies  of  equal  bulk — were  brought  to 
incandescence.  The  three  bulbs  were  sealed  to  a  glass 
tube,  which  was  connected  to  a  Sprengel  pump.  When  a 
high  vacuum  had  been  reached,  the  glass  tube  carrying  the 
bulbs  was  sealed  off.  A  current  was  then  turned  on  suc¬ 
cessively  on  each  bulb,  and  it  was  found  that  the  filaments 
came  to  about  the  same  brightness,  and,  if  anything,  tho 
smallest  bulb,  which  was  placed  midway  between  the  two 
larger  ones,  may  have  been  slightly  brighter.  This  result 
was  expected,  for  when  either  of  the  bulbs  was  connected 
to  the  coil  the  luminosity  spread  through  the  other  two, 
hence  the  three  bulbs  constituted  really  one  vessel.  When 
all  the  three  bulbs  were  connected  in  multiple  arc  to  the 
coil,  in  the  largest  of  them  the  filament  glowed  brightest, 
in  the  next  smaller  it  was  a  little  less  bright,  and  in  the 
smallest  it  only  came  to  redness.  The  bulbs  were  then 
sealed  off  and  separately  tried.  The  brightness  of  the  fil¬ 
aments  was  now  such  as  would  have  been  expected  on  the 
supposition  that  the  energy  given  off  was  proportionate  to 
the  surface  of  the  bulb,  this  surface  in  each  case  represent- 


62 


mg  one  of  the  coatings  of  a  condenser.  Accordingly,  there 
was  less  difference  between  the  largest  and  the  middle  sized 
than  between  the  latter  and  the  smallest  bulb. 

An  interesting  observation  was  made  in  this  experiment. 
The  three  bulbs  were  suspended  fiem  a  straight  bare  wire 
connected  to  a  terminal  of  the  coil,  the  largest  bulb  being 
placed  at  the  end  of  the  wire,  at  some  distance  from  it  the 
smallest  bulb,  and  an  equal  distance  from  the  latter  the 
middle-sized  one.  The  carbons  glowed  then  in  both  the 
larger  bulbs  about  as  expected,  but  the  smallest  did  not  get 
its  share  by  far.  This  observation  led  me  to  exchange  the 
position  of  the  bulbs,  and  I  then  observed  that  whichever 
of  the  bulbs  was  in  the  middle  it  was  by  far  less  bright  than 
it  was  in  any  other  position.  This  mystifying  result  was,  of 
course,  found  to  be  due  to  the  electrostatic  action  between 
the  bulbs.  When  they  were  placed  at  a  considerable  dis¬ 
tance,  or  when  they  were  attached  to  the  corners  of  an 
equilateral  triangle  of  copper  wire,  they  glowed  about  in 
the  order  determined  by  their  surfaces. 

As  to  the  shape  of  the  vessel,  it  is  also  of  some  impor¬ 
tance,  especially  at  high  degrees  of  exhaustion.  Of  all  the 
possible  constructions,  it  seems  that  a  spherical  globe  with 
the  refractory  body  mounted  in  its  centre  is  the  best  to  em¬ 
ploy.  In  experience  it  has  been  demonstrated  that  in  such 
a  globe  a  refractory  body  of  a  given  bulk  is  more  easily 
brought  to  incandescence  than  when  otherwise  shaped 
bulbs  are  used.  There  is  also  an  advantage  in  giving  to  the 
incandescent  body  the  shape  of  a  sphere,  for  self-evident 
reasons.  In  any  case  the  body  should  be  mounted  in  the 
centre,  where  the  atoms  rebounding  from  the  glass  collide. 


63 


This  object  is  best  attained  in  the  spherical  bulb  ;  but  it  is 
also  attained  in  a  cylindrical  vessel  with  one  or  two  straight 
filaments  coinciding  with  its  axis,  and  possibly  also  in  par¬ 
abolical  or  spherical  bulbs  with  the  refractory  body  or 
bodies  placed  in  the  focus  or  foci  of  the  same;  though  the 
latter  is  not  probable,  as  the  electrified  atoms  should  in  all 
cases  rebound  normally  from  the  surface  they  strike,  unless 
the  speed  were  excessive,  in  which  case  they  would  prob¬ 
ably  follow  the  general  law  of  reflection.  No  mat  er  what 
shape  the  vessel  may  have,  if  the  exhaustion  be  low,  a  fila¬ 
ment  mounted  in  the  globe  is  brought  to  the  same  degree 
of  incandescence  in  all  parts;  but  if  the  exhaustion  be  high 
and  the  bulb  be  spherical  or  pear-shaped,  as  usual,  focal 
points  form  and  the  filament  is  heated  to  a  higher  degree 
at  or  near  such  points. 

To  illustrate  the  effect,  I  have  here  two  small  bulbs  which 
are  alike,  only  one  is  exhausted  to  a  low  and  the  other  to  a 
very  high  degree.  When  connected  to  the  coil,  the  fila¬ 
ment  in  the  former  glows  uniformly  throughout  all  its 
length;  whereas  in  the  latter,  that  portion  of  the  filament 
which  is  in  the  centre  of  the  bulb  glows  far  more  intensely 
than  the  rest.  A  curious  point  is  that  the  phenomenon 
occurs  even  if  two  filaments  are  mounted  in  a  bulb,  each 
being  connected  to  one  terminal  of  the  coil,  and,  what  is 
still  more  curious,  if  they  be  very  near  together,  provided 
the  vacuum  be  very  higji.  I  noted  in  experiments  with 
such  bulbs  that  the  filaments  would  give  way  usually  at  a 
certain  point,  and  in  the  first  trials  I  attributed  it  to  a  defect 

in  the  carbon.  But  when  the  phenomenon  occurred  many 
% 

times  in  succession  I  recognized  its  real  cause. 


64 


In  order  to  bring  a  refractory  body  inclosed  in  a  bulb  to 
incandescence,  it  is  desirable,  on  account  of  economy,  that 
all  the  energy  supplied  to  the  bulb  from  the  source 
should  reach  without  loss  the  body  to  be  heated;  from 
there,  and  from  nowhere  else,  it  should  be  radiated.  It  is, 
of  course,  out  of  the  question  to  reach  this  theoretical  re¬ 
sult,  but  it  is  possible  by  a  proper  construe!  ion  of  the  illu¬ 
minating  device  to  approximate  it  more  or  less. 

For  many  reasons,  the  refractory  body  is  placed  in  che 
centre  of  the  bulb,  and  it  is  usually  supported  on  a  glass 
stem  containing  the  leading-in  wire.  As  the  potential  of 
this  wire  is  alternated,  the  rarefied  gas  surrounding  the 
stem  is  acted  upon  inductively,  and  the  glass  stem  is  vio¬ 
lently  bombarded  and  heated.  In  this  manner  by  far  the 
greater  portion  of  the  energy  supplied  to  the  bulb — es¬ 
pecially  when  exceedingly  high  frequencies  are  used — may 
be  lost  for  the  purpose  contemplated.  To  obviate  this  loss, 
or  at  least  to  reduce  it  to  a  minimum,  I  usually  screen  the 
rarefied  gas  surrounding  the  stem  from  the  inductive 
action  of  the  leading-in  wire  by  providing  the  stem 
with  a  tube  or  coating  of  conducting  material.  It 
seems  beyond  doubt  that  the  best  among  metals  to 
employ  for  this  purpose  is  aluminium,  on  account  of 
its  many  remarkable  properties.  Its  only  fault  is  that 
it  is  easily  fusible,  and,  therefore,  its  distance  from  the 
incandescing  body  should  be  properly  estimated.  Usually, 
a  thin  tube,  of  a  diameter  somewhat  smaller  than  that  c  f 
the  glass  stem,  is  made  of  the  finest  aluminium  sheet,  and 
slipped  on  the  stem.  The  tube  is  conveniently  prepared  by 
wrapping  around  a  rod  fastened  in  a  lathe  a  piece  of  alu- 


minium  sheet  of  the  proper  size,  grasping  the  sheet  firmly 
with  clean  chamois  leather  or  blotting  paper,  and  spinning 
the  rod  very  fast.  The  sheet  is  wound  tightly  around  the 
rod,  and  a  highly  polished  tube  of  one  or  three  layers  of  the 
sheet  is  obtainnd.  When  slipped  on  the  stem,  the  pressure 
is  generally  sufficient  to  prevent  it  from  slipping  off,  but, 
for  safety,  the  lower  edge  of  the  sheet  may  be  turned  in¬ 
side.  The  upper  inside  corner  of  the  sheet — that  is,  the 
one  which  is  nearest  to  the  refractory  incandescent  body 
— should  be  cut  out  diagonally,  as  it  often  happens 
that,  in  consequence  of  the  intense  heat,  this 
corner  turns  toward  the  inside  and  comes  very  near 
to,  or  in  contact  with,  the  wire,  or  filament,  supporting  the 
refractory  body.  The  greater  part  of  the  energy  supplied  to 
the  bulb  is  then  used  up  in  heating  the  metal  tube,  anel  the 
bulb  is  rendered  useless  for  the  purpose.  The  aluminium 
sheet  should  project  above  the  glass  stem  more  or  less — one 
inch  or  so — or  else,  if  the  glass  be  too  close  to  the  incandes¬ 
cing  body,  it  may  be  strongly  heated  and  become  more  or 
less  conducting,  whereupon  it  may  be  ruptured,  or  may,  by 
its  conductivity,  establish  a  good  electrical  connection  be¬ 
tween  the  metal  tube  and  the  leading-in  wire,  in  which  case, 
again,  most  of  the  energy  will  be  lost  in  heating  the  former. 
Perhaps  the  best  way  is  to  make  the  top  of  the  glass  tube, 
for  about  an  inch,  of  a  much  smaller  diameter.  To  still 
further  reduce  the  danger  arising  from  the  heating  of  the 
glass  stem,  and  also  with  the  view  of  preventing  an  electric¬ 
al  connection  between  the  metal  tube  and  the  electrode,  I 
preferably  wrap  the  stem  with  several  layers  of  thin  mica, 
which  extends  at  least  as  far  as  the  metal  tube.  In 


66 


some  bulbs  I  have  also  used  an  outside  insulating 
cover. 

The  preceding  remarks  are  only  made  to  aid  the  experi¬ 
menter  in  the  first  trials,  for  the  difficulties  which  he  en¬ 
counters  he  may  soon  find  means  to  overcome  in  his  own 
way. 

To  illustrate  the  effect  of  the  screen,  and  the  advantage 
of  using  it,  I  have  here  two  bulbs  of  the  same  size,  with 
their  stems,  leading-in  wires  and  incandescent  lamp  fila¬ 
ments  tied  to  the  latter,  as  uearly  alike  as  possible.  The 
stem  of  one  bulb  is  provided  with  an  aluminium  tube,  the 
stem  of  the  other  has  none.  Originally  the  two  bulbs  were 
joined  by  a  tube  which  was  connected  to  aSprengel  pump. 
When  a  high  vacuum  had  been  reached,  first  the  connect¬ 
ing  tube,  and  then  the  bulbs,  were  sealed  off ;  they  are 
therefore  of  the  same  degree  of  exhaustion.  When  they 

are  separately  connected  to  the  coil  giving  a  certain  poten- 

« 

tial,  the  carbon  filament  in  the  bulb  provided  with  the 
aluminium  screen  is  rendered  highly  incandescent,  while 
the  filament  in  the  other  bulb  may,  with  the  same  po¬ 
tential,  not  even  come  to  redness,  although  in  reality 
the  latter  bulb  takes  generally  more  energy  than  the 
former.  When  they  are  both  connected  together 
to  the  terminal,  the  difference  is  even  more  ap¬ 
parent,  showing  the  importance  of  the  screening.  The 
metal  tube  placed  on  the  stem  containing  the  leading-in 
wire  performs  really  two  distinct  functions:  First;  it  acts 
more  or  less  as  an  electrostatic  screen,  thus  economizing 
the  energy  supplied  to  the  bulb;  and,  second,  to  whatever 
extent  it  may  fail  to  act  electrostatically,  it  acts  mechanic- 


ally,  preventing  the  bombardment,  and  consequently  in¬ 
tense  heating  and  possible  deterioration  of  the  slender  sup¬ 
port  of  the  refractory  incandescent  body,  or  of  the  glass 
stem  containing  the  leading-in  wire.  I  say  slender  sup¬ 
port,  for  it  is  evident  that  in  order  to  confine  the  heat  more 
completely  to  the  incandescing  body  its  support  should  be 
very  thin,  so  as  to  carry  away  the  smallest  possible  amount 
of  heat  by  conduction.  Of  all  the  supports  used  I  have 
found  an  ordinary  incandescent  lamp  filament  to  be  the 
best,  principally  because  among  conductors  it  can  with¬ 
stand  the  highest  degrees  of  heat. 

The  effectiveness  of  the  metal  tube  as  an  electrostatic 
screen  depends  largely  on  the  degree  of  exhaustion. 

At  excessively  high  degrees  of  exhaustion — which  are 
reached  by  using  great  care  and  special  means  in  connection 
with  the  Sprengel  pump — when  the  matter  in  the  globe  is 
in  the  ultra-radiant  state,  it  acts  most  perfectly.  The  shadow 
of  the  upper  edge  of  the  tube  is  then  sharply  defined  upon 
the  bulb. 

At  a  somewhat  lower  degree  of  exhaustion,  which  is  about 
the  ordinary  “non-striking”  vacuum,  and  generally  as  long 
as  the  matter  moves  predominantly  in  straight  lines,  the 
screen  still  does  well.  In  elucidation  of  the  preceding  re¬ 
mark  it  is  necessary  to  state  that  what  is  a  “non-striking” 
vacuum  for  a  coil  operated,  as  ordinarily,  by  impulses,  or 
currents,  of  lowfrequency,  is  not,  by  far,  so  when  the  coil 
is  operated  by  currents  of  very  high  frequency.  In  such 
case  the  discharge  may  pass  with  great  freedom  through  the 
rarefied  gas  through  which  a  low-frequency  discharge  may 
not  pass,  even  though  the  potential  be  much  higher.  At 


ordinary  atmospheric  pressures  just  the  reverse  rule  Jkolds 
good:  the  higher  the  frequency,  the  less  the  spark  discharge 
is  able  to  jump  between  the  terminals,  especially  if  they  are 
knobs  or  spheres  of  some  size.  I 

Finally,  at  very  low  degrees  of  exhaustion,  when  the  gas 
is  well  conducting,  the  metal  tube  not  only  does  not  act  as 
an  electrostatic  screen,  but  even  is  a  drawback,  aiding  to  a 
considerable  extent  the  dissipation  of  the  energy  laterally 
from  the  leading-in  wire.  This,  of  course,  is  to  be  expected. 
In  this  case,  namely,  the  metal  tube  is  in  good  electrical 
connection  wdth  the  leading-in  wire,  and  most  of  the  bom¬ 
bardment  is  directed  upon  the  tube.  As  long  as  the  elec¬ 
trical  connection  is  not  good,  the  conducting  tube  is  always 

of  some  advantage,  for  although  it  may  not  greatly  econo- 

•  ^  v* 

mize  energy,  still  it  protects  the  support  of  the  refractory 
button,  and  is  a  means  for  concentrating  more  energy  upon 
the  same. 

To  whatever  extent  the  aluminium  tube  performs  the  func¬ 
tion  of  a  screen,  its  usefulness  is  therefore  limited  to  very  high 
degrees  of  exhaustion  when  it  is  insulated  from  the  elec¬ 
trode — that  is,  when  the  gas  as  a  whole  is  non-conducting, 
and  the  molecules,  or  atoms,  act  as  independent  carriers  of 
electric  charges. 

In  addition  to  acting  as  a  more  or  less  effective  screen,  in 
the  true  meaning  of  the  word,  the  conducting  tube  or  coat¬ 
ing  may  also  act,  by  reason  of  its  conductivity,  as  a  sort 
of  equalizer  or  dampener  of  the  bombardment  against  the 
stem.  To  be  explicit,  I  assume  the  action  as  follows  :  Sup¬ 
pose  a  rhythmical  bombardment  to  occur  against  the  con¬ 
ducting  tube  by  reason  of  its  imperfect  action  as  a  screen. 


60 


it  certainly  must  happen  that  some  molecules,  or  atoms, 
strike  the  tube  sooner  than  others.  Those  which  come  first 
in  contact  with  it  give  up  their  superfluous  charge, 
and  the  tube  is  electrified,  the  electrification  in¬ 
stantly  spreading  over  its  surface.  But  this  must 
diminish  the  energy  lost  in  the  bombardment  for  two 
reasons:  first,  the  charge  given  up  by  the  atoms  spreads 
over  a  great  area,  and  hence  the  electric  density  at  any 
point  is  small,  and  the  atoms  are  repelled  with  less  energy 
than  they  would  be  i  f  they  would  strike  against  a  good  in¬ 
sulator;  secondly,  as  the  tube  is  electrified  by  the  atoms 
which  first  come  in  contact  with  it,  the  progress  of  the  fol¬ 
lowing  atoms  against  the  tube  is  more  or  less  checked  by 
the  repulsion  which  the  electrified  tube  must  exert  upon 
the  similarly  electrified  atoms.  This  repulsion  may  per¬ 
haps  be  sufficient  to  prevent  a  large  portion  of  the  atoms 
from  striking  the  tube,  bat  at  any  rate  it  must  diminish  the 
energy  of  their  impact.  It  is  clear  that  when  the  exhaus¬ 
tion  is  very  low,  and  the  rarefied  gas  well  conducting, 
neither  of  the  above  effects  can  occur,  and,  on  the  other 
hand,  the  fewer  the  atoms,  with  the  greater  freedom  they 
move;  in  other  words,  the  higher  the  degree  of  exhaustion, 
up  to  a  limit,  the  more  telling  will  be  both  the  effects. 

What  I  have  just  said  may  afford  an  explanation  of  the 
phenomenon  observed  by  Prof.  Crookes,  namely,  that  a 
discharge  through  a  bulb  is  established  with  much  greater 
facility  when  an  insulator  than  when  a  conductor  is  pres¬ 
ent  in  the  same.  In  my  opinion,  the  conductor  acts  as  a 
dampener  of  the  motion  of  the  atoms  in  the  two  ways 
pointed  out;  hence,  to  cause  a  visible  discharge  to  pass 


70 


through  the  bulb,  a  much  higher  potential  is  needed  if  a 
conductor,  especially  of  much  surface,  be  present. 

For  the  sake  of  clearness  of  some  of  the  remarks  before 
made,  I  must  now  refer  to  Figs.  18,  19  and  20,  which  illus¬ 
trate  various  arrangements  with  a  type  of  bulb  most  gen¬ 
erally  used. 


Fig.  18.— Bulb  with  Mica  Fig.  19.— Improved  Bulb 
Tube  and  Aluminium  with  Socket  and 
Screen.  Screen. 

Fig.  18  is  a  section  through  a  spherical  bulb  L,  with 
the  glass  stem  s,  containing  the  leading-in  wire  w,  which 
has  a  lamp  filament  l  fastened  to  it,  serving  to  support  the 
refractory  button  m  in  the  centre.  M  is  a  sheet  of  thin 


71 

mica  wound  in  several  layers  around  the  stem  s,  and  a  is 
the  aluminium  tube. 

Fig.  19  illustrates  such  a  bulb  in  a  somewhat  more  ad¬ 
vanced  stage  of  perfection.  A  metallic  tube  S  is  fastened 
by  means  of  some  cement  to  the  neck  of  the  tube.  In  the 
tube  is  screwed  a  plug  P,  of 
insulating  material,  in  the 
centre  of  which  is  fastened  a 
metallic  terminal  t,  for  the 
connection  to  the  leading-in 
wire  w.  This  terminal  must 
be  well  insulated  from  the 
metal  tube  S ,  therefore,  if  the 
cement  used  is  conducting — 
and  most  generally  it  is  suf¬ 
ficiently  so — the  space  between 
the  plug  P  and  the  neck  of 
the  bulb  should  be  filled  with 
some  good  insulating  material, 
as  mica  powder. 

Fig.  20  shows  a  bulb  made 

for  experimental  purposes.  In 

this  bulb  the  aluminium  tube  ^IG*  20.— Bule  for  Experi¬ 
ments  with  Conducting 
is  provided  with  an  external  Tube. 

connection,  which  serves  to  investigate  the  effect  of  the 

tube  under  various  conditions.  It  is  referred  to  chiefly  to 

suggest  a  line  of  experiment  followed. 

Since  the  bombardment  against  the  stem  containing  the 
leading-in  wire  is  due  to  the  inductive  action  of  the  latter 
upon  the  rarefied  gas,  it  is  of  advantage  to  reduce  this  ac- 


72 

tion  as  far  as  practicable  by  employing  a  very  thin  wire, 
*  surrounded  by  a  very  thick  insulation  of  glass  or  other  ma¬ 
terial,  and  by  making  the  wire  passing  through  the  rarefied 
gas  as  short  as  practicable.  To  combine  these  features  I 
employ  a  large  tube  T  (Fig.  21),  which  protrudes  into  the 
bulb  to  some  distance,  and  carries  on  the  top  a  very  short 
glass  stem  s,  into  which  is  sealed  the  leading-in  wire  w, 
and  I  protect  the  top  of  the  glass  stem  against  the  heat  by  a 
small,  aluminium  tube  a  and  a  layer  of  mica  underneath 
the  same,  as  usual.  The  wire  w ,  passing  through  the  large 
tube  to  the  outside  of  the  bulb,  should  be  well  insulated — 
with  a  glass  tube,  for  instance — and  the  space  between 
ought  to  be  filled  out  with  some  excellent  insulator.  Among 
many  insulating  powders  I  have  tried,  I  have  found  that 
mica  powder  is  the  best  to  employ.  If  this  precaution  is 
not  taken,  the  tube  T,  protruding  into  the  bulb,  will  surely 
be  cracked  in  consequence  of  the  heating  by  the  brushes 
which  are  apt  to  form  in  the  upper  part  of  the  tube,  near 
the  exhausted  globe,  especially  if  the  vacuum  be  excellent, 
and  therefore  the  potential  necessary  to  operate  the  lamp 
very  high. 

Fig.  22  illustrates  a  similar  arrangement,  with  a  large 
tube  T  protruding  into  the  part  of  the  bulb  containing  the 
refractory  button  m.  In  this  case  the  wire  leading  from 
the  outside  into  the  bulb  is  omitted,  the  energy  required 
being  supplied  through  condenser  coatings  C  C.  The  insulat¬ 
ing  packing  P  should  in  this  construction  be  tightly  fitting 
to  the  glass,  and  rather  wide,  or  otherwise  the  discharge 
might  avoid  passing  through  the  wire  w,  which  connects 
the  inside  condenser  coating  to  the  incandescent  button  in. 


73 


The  molecular  bombardment  against  the  glass  stem  in 


the  bulb  is  a  source  of  great  trouble.  As  illustration  I  will 
cite  a  phenomenon  only  too  frequently  and  unwillingly 
observed.  A  bulb,  preferably  a  large  one,  may  be  taken, 


O 

Fig.  21.— Improved  Bulb 
with  Non-Conducting 
Button. 


without  Leading-In 
Wire. 


and  a  good  conducting  body,  such  as  a  piece  of  carbon,  may 
be  mounted  in  it  upon  a  platinum  wire  sealed  in  the  glass 
stem.  The  bulb  may  be  exhausted  to  a  fairly  high  degree, 
nearly  to  the  point  when  phosphorescence  begins  to  appear. 


When  the  bulb  is  connected  with  the  coil,  the  piece  of 
carbon,  if  small,  may  become  highly  incandescent  at  first, 
but  its  brightness  immediately  diminishes,  and  then  the 
discharge  may  break  through  the  glass  somewhere  in  the 
middle  of  the  stem,  in  the  form  of  bright  sparks,  in  spite  of 
the  fact  that  the  platinum  wire  is  in  good  electrical  con¬ 
nection  with  the  rarefied  gas  through  the  piece  of  carbon  or 
metal  at  the  top.  The  first  sparks  are  singularly  bright, 
recalling  those  drawn  from  a  clear  surface  of  mercury. 
But,  as  they  heat  the  glass  rapidly,  they,  of  course,  lose  their 
brightness,  and  cease  when  the  glass  at  the  ruptured  place 
becomes  incandescent,  or  generally  sufficiently  •  hot  to  con¬ 
duct.  |  When  observed  for  the  first  time  the  phenomenon 
must  appear  very  curious,  and  shows  in  a  striking  manner 
how  radically  different  alternate  currents,  or  impulses,  of 
high  frequency  behave,  as  compared  with  steady  currents, 
or  currents  of  low  frequency^  With  such  currents — namely, 
the  latter — the  phenomenon  would  of  course  not  occur. 
When  frequencies  such  as  are  obtained  by  mechanical 
means  are  used,  I  think  that  the  rupture  of  the  glass  is 
more  or  less  the  consequence  of  the  bombardment,  which 
warms  it  up  and  impairs  its  insulating  power;  but  with 
frequencies  obtainable  with  condensers  I  have  no  doubt 
that  the  glass  may  give  way  without  previous  heating.  Al¬ 
though  this  appears  most  singular  at  first,  it  is  in  reality 
what  we  might  expect  to  occur.  The  energy  supplied  to 
the  wire  leading  into  the  bulb  is  given  off  partly  by  direct 
action  through  the  carbon  button,  and  partly  by  inductive 
action  through  the  glass  surrounding  the  wire.  The  case 
is  thus  analogous  to  that  in  which  a  condenser  shunted  by  a 


75 


conductor  of  low  resistance  is  connected  to  a  source  of  al¬ 
ternating  currents.  As  long  as  the  frequencies  are  low, 
the  conductor  gets  the  most,  and  the  condenser  is  perfectly 
safe;  but  when  the  frequency  becomes  excessive,  the  role 
of  the  conductor  may  become  quite  insignificant.  In  the 


Fig.  23.— Effect  Produced  by  a  Ruby  Drop. 

latter  case  the  difference  of  potential  at  the  terminals  of 
the  condenser  may  become  so  great  as  to  rupture  the  di¬ 
electric,  notwithstanding  the  fact  that  the  terminals  are 
joined  by  a  conductor  of  low  resistance, 


76 


It  is,  of  course,  not  necessary,  when  it  is  desired  to  pro¬ 
duce  the  incandescence  of  a  body  inclosed  in  a  bulb  by 
means  of  these  currents,  that  the  body  should  be  a  con¬ 
ductor,  for  even  a  perfect  non-conductor  may  be  quite  as 
readily  heated.  For  this  purpose  it  is  sufficient  to  sur¬ 
round  a  conducting  electrode  with  a  non-conducting  ma¬ 
terial,  as,  for  instance,  in  the  bulb  described  before  in  Fig. 
21,  in  which  a  thin  incandescent  lamp  filament  is  coated 
with  a  non-conductor,  and  supports  a  button  of  the  same 
material  on  the  top.  At  the  start  the  bombardment  goes 
on  by  inductive  action  through  the  non-conductor,  until 
the  same  is  sufficiently  heated  to  become  conducting,  when 
the  bombardment  continues  in  the  ordinary  way. 

A  different  arrangement  used  in  some  of  the  bulbs  con¬ 
structed  is  illustrated  in  Fig.  23.  In  this  instance  a  non-con¬ 
ductor  m  is  mounted  in  a  piece  of  common  arc  light  carbon  so 
as  to  project  some  small  distance  above  the  latter.  The  car¬ 
bon  piece  is  connected  to  the  leading-in  wire  passing 
through  a  glass  stem,  which  is  wrapped  with  several  layers 
of  mica.  An  aluminium  tube  a  is  employed  as  usual  for 
screening.  It  is  so  arranged  that  it  reaches  very  nearly  as 
high  as  the  carbon  and  only  the  non-conductor  m  projects 
a  little  above  it.  The  bombardment  goes  at  first  against 
the  upper  surface  of  carbon,  the  lower  parts  being  protect¬ 
ed  by  the  aluminium  tube.  As  soon,  however,  as  the  non¬ 
conductor  m  is  heated  it  is  rendered  good  conducting,  and 
then  it  becomes  the  centre  of  the  bombardment,  being  most 
exposed  to  the  same. 

I  have  also  constructed  during  these  experiments  many 
such  single-wire  bulbs  with  or  without  internal  electrode, 


77 


in  which  the  radiant  matter  was  projected  against,  or  fo¬ 
cused  upon,  the  body  to  be  rendered  incandescent.  Fig.  24 
illustrates  one  of  the  bulbs  used.  It  consists  of  a  spherical 
globe  L,  provided  with  a  long  neck  n,  on  the  top,  for  in¬ 
creasing  the  action  in  some  cases  by  the  application  of  an 
external  conducting  coating.  The  globe  L  is  blown  out  on 
the  bottom  into  a  very  small  bulb  5*  which  serves  to  hold 
it  firmly  in  a  socket  S  of  insulating  material  into  which 
it  is  cemented.  A  fine  lamp  filament  /,  supported  on  a 
wire  w,  passes  through  the  centre  of  the  globe  L.  The 
filament  is  rendered  incandescent  in  the  middle  portion, 
where  the  bombardment  proceeding  from  the  lower  inside 
surface  of  the  globe  is  most  intense.  The  lower  portion  of 
the  globe,  as  far  as  the  socket  S  reaches,  is  rendered  con¬ 
ducting,  either  by  a  tinfoil  coating  or  otherwise,  and  the 
external  electrode  is  connected  to  a  terminal  of  the  coil. 

The  arrangement  diagram matically  indicated  in  Fig.  24 
was  found  to  be  an  inferior  one  when  it  was  desired  to  ren¬ 
der  incandescent  a  filament  or  button  supported  in  the 
centre  of  the  globe,  but  it  was  convenient  when  the  object 
was  to  excite  phosphorescence. 

In  many  experiments  in  which  bodies  of  a  different  kind 
were  mounted  in  the  bulb  as,  for  instance,  indicated  in 
Fig.  23,  some  observations  of  interest  were  made. 

It  was  found,  among  other  things,  that  in  such  cases,  no 
matter  where  the  bombardment  began,  just  as  soon  as  a 
high  temperature  was  reached  there  was  generally  one  of 
the  bodies  which  seemed  to  take  most  of  the  bombardment 
upon  itself,  the  other,  or  others,  being  thereby  relieved. 
This  quality  appeared  to  depend  principally  on  the  point  of 


78 


fusion,  and  on  the  facility  with  which  the  body  was 
“evaporated,”  or,  generally  speaking,  disintegrated — mean- 
ing  by  the  latter  term  not  only  the  throwing  off  of  atoms, 
but  likewise  of  larger  lumps.  The  observation  made  was 
in  accordance  with  generally  accepted  notions.  In  a  highly 
exhausted  bulb  electricity  is  carried  off  from  the  electrode 
by  independent  carriers,  which  are  partly  the  atoms,  or 
molecules,  of  the  residual  atmosphere,  and  partly  the  atoms, 
molecules,  or  lumps  thrown  off  from  the  electrode.  If  the 
electrode  is  composed  of  bodies  of  different  character,  and 
if  one  of  these  is  more  easily  disintegrated  than  the  others, 
most  of  the  electricity  supplied  is  carried  off  from  that  body, 
which  is  then  brought  to  a  higher  temperature  than  the 
others,  and  this  the  more,  as  upon  an  increase  of  the  tem¬ 
perature  the  body  is  still  more  easily  disintegrated. 

It  seems  to  me  quite  probable  that  a  similar  process  takes 
place  in  the  bulb  even  with  a  homogeneous  electrode,  and 
I  think  it  to  be  the  principal  cause  of  the  disintegration. 
There  is  bound  to  be  some  irregularity,  even  if  the  surface 
is  highly  polished,  which,  of  course,  is  impossible  with  most 
of  the  refractory  bodies  employed  as  electrodes.  Assume 
that  a  point  of  the  electrode  gets  hotter,  instantly  most  of 
the  discharge  passes  through  that  point,  and  a  minute  patch 
is  probably  fused  and  evaporated.  It  is  now  possible  that  in 
consequence  of  the  violent  disintegration  the  spot  attacked 
sinks  in  temperature,  or  that  a  counter  force  is  created,  as 
in  an  arc;  at  any  rate,  the  local  tearing  off  meets 
with  the  limitations  incident  to  the  experiment,  where¬ 
upon  the  same  process  occurs  on  another  place.  To 
the  eye  the  electrode  appears  uniformly  brilliant. 


79 


79 

but  there  are  upon  it  points  constantly  shiftin 
wandering  around,  of  a  temperature  far  above 
mean,  and  this  materially  hastens  the  process  of  deteriora¬ 
tion.  That  some  such  thing  occurs,  at  least  when  the  elec¬ 
trode  is  at  a  lower  temperature,  sufficient  experimental  evi¬ 
dence  can  be  obtained  in  the  following  manner  :  Exhaust  a 
bulb  to  a  very  high  degree,  so  that  with  a  fairly  high  poten¬ 
tial  the  discharge  cannot  pass — that  is,  not  a  luminous  one, 
for  a  weak  invisible  discharge  occurs  always,  in  all  prob¬ 
ability.  Now  raise  slowly  and  carefully  the  potential,  leav¬ 
ing  the  primary  current  on  no  more  than  for  an  instant.  At 
a  certain  point,  two,  three,  or  half  a  dozen  phosphorescent 
spots  will  appear  on  the  globe.  These  places  of  the  glass  are 
evidently  more  violently  bombarded  than  others,  this  being 
due  to  the  unevenly  distributed  electric  density,  necessitated, 
of  course,  by  sharp  projections,  or,  generally  speaking,  ir¬ 
regularities  of  the  electrode.  But  the  luminous  patches  are 
constantly  changing  in  position,  which  is  especially  well  ob¬ 
servable  if  one  manages  to  produce  very  few,  and  this  in¬ 
dicates  that  the  configuration  of  the  electrode  is  rapidly 
changing. 

From  experiences  of  this  kind  I  am  led  to  infer  that, 
in  order  to  be  most  durable,  the  refractory  button  in  the 
bulb  should  be  in  the  form  of  a  sphere  with  a  highly 
polished  surface.  Such  a  small  sphere  could  be  manu¬ 
factured  from  a  diamond  or  some  other  crystal,  but  a  bet¬ 
ter  way  would  be  to  fuse,  by  the  employment  of  extreme 
degrees  of  temperature,  some  oxide — as,  for  instance,  zir- 
conia — into  a  small  drop,  and  then  keep  it  in  the  bulb  at  a 
temperature  somewhat  below  its  point  of  fusion. 


80 


* 


Interesting  and  useful  results  can  no  doubt  be  reached  in 
the  direction  of  extreme  degrees  of  heat.  How  can  such 
high  temperatures  be  arrived  at  ?  How  are  the  highest 
degrees  of  heat  reached  in  nature  ?  By  the  impact  of 
stars,  by  high  speeds  and  collisions.  In  a  collision  any 
rate  of  heat  generation  may  be  attained.  In  a  chemical 
process  we  are  limited.  When  oxygen  and  hydrogen  com¬ 
bine,  they  fall,  metaphorically  speaking,  from  a  definite 
height.  We  cannot  go  very  far  with  a  blast,  nor  by  con¬ 
fining  heat  in  a  furnace,  but  in  an  exhausted  bulb  we  can 
concentrate  any  amount  of  energy  upon  a  minute  button. 
Leaving  practicability  out  of  consideration,  this,  then, 
would  be  the  means  which,  in  my  opinion,  would  enable 
us  to  reach  the  highest  temperature.  But  a  great  difficulty 
when  proceeding  in  this  way  is  encountered,  namely,  in 
most  cases  the  body  is  carried  off  before  it  can  fuse  and 
form  a  drop.  This  difficulty  exists  principally  with  an  ox¬ 
ide  such  as  zirconia,  because  it  cannot  be  compressed  in  so 
hard  a  cake  that  it  would  not  be  carried  off  quickly.  .  I  en¬ 
deavored  repeatedly  to  fuse  zirconia,  placing  it  in  a  cup  or 
arc  light  carbon  as  indicated  in  Fig.  23.  It  glowed  with  a 
most  intense  light,  and  the  stream  of  the  particles  project¬ 
ed  out  of  the  carbon  cup  was  of  a  vivid  white;  but  whether 
it  was  compressed  in  a  cake  or  made  into  a  paste  with  • 
carbon,  it  was  carried  off  before  it  could  be  fused.  The 
carbon  cup  containing  the  zirconia  had  to  be  mounted  very 
low  in  the  neck  of  a  large  bulb,  as  the  heating  of  the  glass 
by  the  projected  particles  of  the  oxide  was  so  rapid  that  in 
the  first  trial  the  bulb  was  cracked  almost  in  an  instant 
when  the  current  was  turned  on.  The  heating  of  the  glass 


81 


by  the  projected  particles  was  found  to  be  always  greater 
when  the  carbon  cup  contained  a  body  which  was  rapidly 
carried  off — I  presume  because  in  such  cases,  with  the  same 
potential,  higher  speeds  were  reached,  and  also  because, 
per  unit  of  time,  more  matter  was  projected — that  is,  more 
particles  would  strike  the  glass. 

The  before  mentioned  difficulty  did  not  exist,  however, 
when  the  body  mounted  in  the  carbon  cup  offered  great  re¬ 
sistance  to  deterioration.  For  instance,  when  an  oxide  was 
first  fused  in  an  oxygen  blast  and  then  mounted  in  the  bulb, 
it  melted  very  readily  into  a  drop. 

Generally  during  the  process  of  fusion  magnificent  light 
effects  were  noted,  of  which  it  would  be  difficult  to  give  an 
adequate  idea.  Fig.  28  is  intended  to  illustrate  the  effect 
observed  with  a  ruby  drop.  At  first  one  may  see  a  narrow 
funnel  of  white  light  projected  against  the  top  of  the  globe, 
where  it  produces  an  irregularly  outlined  phosphorescent 
patch.  When  the  point  of  the  ruby  fuses  the  phosphores¬ 
cence  becomes  very  powerful ;  but  as  the  atoms  are  pro¬ 
jected  with  much  greater  speed  from  the  surface  of  the 
drop,  soon  the  glass  gets  hot  and  “tired,”  and  now  only  the 
outer  edge  of  the  patch  glows.  In  this  manner  an  intensely 
phosphorescent,  sharply  defined  line,  l,  corresponding  to 
the  outline  of  the  drop,  is  produced,  which  spreads  slowly 
over  the  globe  as  the  drop  gets  larger.  When  the  mass  be¬ 
gins  to  boil,  small  bubbles  and  cavities  are  formed,  which 
cause  dark  colored  spots  to  sweep  across  the  globe.  The 
bulb  may  be  turned  downward  without  fear  of  the  drop 
falling  off,  as  the  mass  possesses  considerable  viscosity. 

I  may  mention  here  another  feature  of  some  interest, 


82 

which  I  believe  to  have  noted  in  the  course  of  these  ex¬ 
periments,  though  the  observations  do  not  amount  to  a 
certitude.  It  appeared  that  under  the  molecular  impact 
caused  by  the  rapidly  alternating  potential  the  body  was 
fused  and  maintained  in  that  state  at  a  lower  temperature 
in  a  highly  exhausted  bulb  than  was  the  case  at  normal 
pressure  and  application  of  heat  in  the  ordinary  way — 
that  is,  at  least,  judging  from  the  quantity  of  the  light 
emitted.  One  of  the  experiments  performed  may  be  men¬ 
tioned  here  by  way  of  illustration.  A  small  piece  of 
pumice  stone  was  stuck  on  a  platinum  wire,  and  first 
melted  to  it  in  a  gas  burner.  The  wire  was  next  placed 
between  two  pieces  of  charcoal  and  a  burner  applied  so  as 
to  produce  an  intense  heat,  sufficient  to  melt  down  the 
pumice  stone  into  a  small  glass-like  button.  The  platinum 
wire  had  to  be  taken  of  sufficient  thickness  to  prevent 
its  melting  in  the  fire.  While  in  the  charcoal  fire,  or  when 
held  in  a  burner  to  get  a  better  idea  of  the  degree  of  heat, 
the  button  glowed  with  great  brilliancy.  The  wire  with 
the  button  was  then  mounted  in  a  bulb,  and  upon  exhaust¬ 
ing  the  same  to  a  high  degree,  the  current  was  turned  on 
slowly  so  as  to  prevent  the  cracking  of  the  button.  The 
button  was  heated  to  the  point  of  fusion,  and  when  it 
melted  it  did  not,  apparently,  glow  with  the  same  brilliancy 
as  before,  and  this  would  indicate  a  lower  temperature. 
Leaving  out  of  consideration  the  observer’s  possible,  and 
even  probable,  error,  the  question  is,  can  a  body  under 
these  conditions  be  brought  from  a  solid  to  a,  liquid  state 
with  evolution  of  less  light  ? 

When  the  potential  of  a  body  is  rapidly  alternated  it  is 


88 


certain  that  the  structure  is  jarred.  When  the  potential  is 
very  high,  although  the  vibrations  may  be  few — say  20,000 
per  second — the  effect  upon  the  structure  may  be  consider¬ 
able.  Suppose,  for  example,  that  a  ruby  is  melted  into  a 
drop  by  a  steady  application  of  energy.  When  it  forms  a 
drop  it  will  emit  visible  and  invisible  waves,  which  will  be 
in  a  definite  ratio,  and  to  the  eye  the  drop  will  appear  to  be 
of  a  certain  brilliancy.  Next,  suppose  we  diminish  to  any 
degree  we  choose  the  energy  steadily  supplied,  and,  in¬ 
stead,  supply  energy  which  rises  and  falls  according  to  a 
certain  law.  Now,  when  the  drop  is  formed,  there  will  be 
emitted  from  it  three  different  kinds  of  vibrations — the  or¬ 
dinary  visible,  and  two  kinds  of  invisible  waves  :  that  is, 
the  ordinary  dark  waves  of  all  lengths,  and,  in  addition, 
waves  of  a  well  defined  character.  The  latter  would  not 
exist  by  a  steady  supply  of  the  energy ;  still  they  help  to 
jar  and  loosen  the  structure.  If  this  really  be  the  case, 
then  the  ruby  drop  will  emit  relatively  less  visible  and 
more  invisible  waves  than  before.  Thus  it  would  seem 
that  when  a  platinum  wire,  for  instance,  is  fused  by  cur¬ 
rents  alternating  with  extreme  rapidity,  it  emits  at  the 
point  of  fusion  less  light  and  more  invisible  radiation  than 
it  does  when  melted  by  a  steady  current,  though  the  total 
energy  used  up  in  the  process  of  fusion  is  the  same  in  both 
cases.  Or,  to  cite  another  example,  a  lamp  filament  is 
not  capable  of  withstanding  as  long  with  currents  of 
extreme  frequency  as  it  does  with  steady  currents, 
assuming  that  it  be  worked  at  the  same  luminous  intensity. 
This  means  that  for  rapidly  alternating  currents  the  fila¬ 
ment  should  be  shorter  and  thicker.  The  higher  the  fre- 


84 

quency — that  is,  the  greater  the  departure  from  the  steady 
flow — the  worse  it  would  be  for  the  filament.  But  if  the 
truth  of  this  remark  were  demonstrated,  it  would  be  erro¬ 
neous  to  conclude  that  such  a  refractory  button  as  used  in 
these  bulbs  would  be  deteriorated  quicker  by  currents  of 
extremely  high  frequency  than  by  steady  or  low  frequency 
currents.  From  experience  I  may  say  that  just  the  oppo¬ 
site  holds  good:  the  button  withstands  the  bombardment 
better  with  currents  of  very  high  frequency.  But  this  is 
due  to  the  fact  that  a  high  frequency  discharge  passes 
through  a  rarefied  gas  with  much  greater  freedom  than  a 
steady  or  low  frequency  discharge,  and  this  will  say  that 
with  the  former  we  can  work  with  a  lower  potential  or 
with  a  less  violent  impact.  As  long,  then,  as  the  gas  is  of 
no  consequence,  a  steady  or  low  frequency  current  is  bet¬ 
ter;  but  as  soon  as  the  action  of  the  gas  is  desired  and  im¬ 
portant,  high  frequencies  are  preferable. 

In  the  course  of  these  experiments  a  great  many  trials 
were  made  with  all  kinds  of  carbon  buttons.  Electrodes 
made  of  ordinary  carbon  buttons  were  decidedly  more 
durable  when  the  buttons  were  obtained  by  the  application 
of  enormous  pressure.  Electrodes  prepared  by  depositing 
carbon  in  well  known  ways  did  not  show  up  well ;  they 
blackened  the  globe  very  quickly.  From  many  experi¬ 
ences  I  conclude  that  lamp  filaments  obtained  in  this 
manner  can  be  advantageously  used  only  with  low 
potentials  and  low  frequency  currents.  Some  kinds  of 
carbon  withstand  so  well  that,  in  order  to  bring  them  to 
the  point  of  fusion,  it  is  necessary  to  employ  very  small 
buttons.  In  this  case  the  observation  is  rendered  very 


85 


difficult  on  account  of  the  intense  heat  produced.  Never¬ 
theless  there  can  be  no  doubt  that  all  kinds  of  carbon  are 
fused  under  the  molecular  bombardment,  but  the  liquid 
state  must  be  one  of  great  instability.  Of  all  the  bodies 
tried  there  were  two  which  withstood  best — diamond  and 
carborundum.  These  two  showed  up  about  equally,  but 
the  latter  was  preferable,  for  many  reasons.  As  it  is  more 
than  likely  that  this  body  is  not  yet  generally  known,  I 
will  venture  to  call  your  attention  to  it. 

It  has  been  recently  produced  by  Mr.  E.  G.  Aclieson,  of 
Monongahela  City,  Pa.,  U.  S.  A.  It  is  intended 
to  replace  ordinary  diamond  powder  for  polishing  precious 
stones,  etc. ,  and  I  have  been  informed  that  it  accomplishes 
this  object  quite  successfully.  I  do  not  know  why  the 
name  “  carborundum  ”  has  been  given  to  it,  unless  there  is 
something  in  the  process  of  its  manufacture  which  justifies 
this  selection.  Through  the  kindness  of  the  inventor,  I 
obtained  a  short  while  ago  some  samples  which  I  desired  to 
test  in  regard  to  their  qualities  of  phosphorescence  and 
capability  of  withstanding  high  degrees  of  heat. 

Carborundum  can  be  obtained  in  two  forms — in  the  form 
of  “crystals”  and  of  powder.  The  former  appear  to  the 
naked  eye  dark  colored,  but  are  very  brilliant ;  the  latter  is 
of  nearly  the  same  color  as  ordinary  diamond  powder,  but 
very  much  finer.  When  viewed  under  a  microscope  the 
samples  of  crystals  given  to  me  did  not  appear  to  have  any 
definite  form,  but  rather  resembled  pieces  of  broken  up  egg 
coal  of  fine  quality.  The  majority  were  opaque,  but  there 
were  some  which  were  transparent  and  colored.  The  crystals 
are  a  kind  of  carbon  containing  some  impurities  ;  they  are 


86 


extremely  hard,  and  withstand  for  a  long  time  even  an 
oxygen  blast.  When  the  blast  is  directed  against  them 
they  at  first  form  a  cake  of  some  compactness,  probably  in 
consequence  of  the  fusion  of  impurities  they  contain.  The 
mass  withstands  for  a  very  long  time  the  blast  without 
further  fusion  ;  but  a  slow  carrying  off,  or  burning,  occurs, 
and,  finally,  a  small  quantity  of  a  glass-like  residue  is  left, 
which,  I  suppose,  is  melted  alumina.  When  compressed 
strongly  they  conduct  very  well,  but  not  as  well  as  ordinary 
carbon.  The  powder,  which  is  obtained  from  the  crystals 
in  some  way,  is  practically  non-conducting.  It  affords  a 
magnificent  polishing  material  for  stones. 

The  time  has  been  too  short  to  make  a  satisfactory  study 
of  the  properties  of  this  product,  but  enough  experience 
has  been  gained  in  a  few  weeks  I  have  experimented  upon 
it  to  say  that  it  does  possess  some  remarkable  properties  in 
many  respects.  It  withstands  excessively  high  degrees  of 
heat,  it  is  little  deteriorated  by  molecular  bombardment, 
and  it  does  not  blacken  the  globe  as  ordinary  carbon  does. 
The  only  difficulty  which  I  have  found  in  its  use  in  connec¬ 
tion  with  these  experiments  was  to  find  some  binding  ma¬ 
terial  which  would  resist  the  heat  and  the  effect  of  the 
bombardment  as  successfully  as  carborundum  itself  does. 

I  have  here  a  number  of  bulbs  which  1  have  provided 
with  buttons  of  carborundum.  To  make  such  a  button  of 
carborundum  crystals  I  proceed  in  the  following  manner  : 
I  take  an  ordinary  lamp  filament  and  dip  its  point  in  tar, 
or  some  other  thick  substance  or  paint  which  may  be  readi¬ 
ly  carbonized.  I  next  pass  the  point  of  the  filament 
through  the  crystals,  and  then  hold  it  vertically  over  a  hot 


87 


% 


plate.  The  tar  softens  and  forms  a  drop  on  the  point  of 
the  filament,  the  crystals  adhering  to  the  surface  of  the 
drop.  By  regulating  the  distance  from  the  plate  the  tar  is 
slowly  dried  out  and  the  button  becomes  solid.  I  then  once 
more  dip  the  button  in  tar  and  hold  it  again  over  a  plate 
until  the  tar  is  evaporated,  leaving  only  a  hard  mass  which 
firmly  binds  the  crystals.  When  a  larger  button  is  required 
I  repeat  the  process  several  times,  and  I  generally  also 
cover  the  filament  a  certain  distance  below  the  button  with 
crystals.  The  button  being  mounted  in  a  bulb,  when  a 
good  vacuum  has  been  reached,  first  a  weak  and  then  a 
strong  discharge  is  passed  through  the  bulb  to  carbonize 
the  tar  and  expel  all  gases,  and  later  it  is  brought  to  a  very 
intense  incandescence. 

When  the  powder  is  used  I  have  found  it  best  to  proceed 
as  follows:  I  make  a  thick  paint  of  carborundum  and  tar, 
and  pass  a  lamp  filament  through  the  paint.  Taking  then 
most  of  the  paint  off  by  rubbing  the  filament  against  a 
piece  of  chamois  leather,  I  hold  it  over  a  hot  plate  until  the 
tar  evaporates  and  the  coating  becomes  firm.  I  repeat  this 
process  as  many  times  as  it  is  necessary  to  obtain  a  certain 
thickness  of  coating.  On  the  point  of  the  coated  filament 
1  form  a  button  in  the  same  manner. 

There  is  no  doubt  that  such  a  button — properly  prepared 
under  great  pressure — of  carborundum,  especially  of 
powder  of  the  best  quality,  will  withstand  the  effect  of  the 
bombardment  fully  as  well  as  anything  we  know.  The 
difficulty  is  that  the  binding  material  gives  way,  and  the 
carborundum  is  slowly  thrown  off  after  some  time.  As  it 
does  not  seem  to  blacken  the  globe  in  the  least,  it  might  be 


88 


found  useful  for  coating  the  filaments  of  ordinary  incan¬ 
descent  lamps,  and  I  think  that  it  is  even  possible  to  pro¬ 
duce  thin  threads  or  sticks  of  carborundum  which  will  re¬ 
place  the  ordinary  filaments  in  an  incandescent  lamp.  A 
carborundum  coating  seems  to  be  more  durable  than  other 
coatings,  not  only  because  the  carborundum  can  withstand 
high  degrees  of  heat,  but  also  because  it  seems  to  unite 
with  the  carbon  better  than  any  other  material  I  have  tried. 
A  coating  of  zirconia  or  any  other  oxide,  for  instance,  is 
far  more  quickly  destroyed.  I  prepared  buttons  of  dia¬ 
mond  dust  in  the  same  manner  as  of  carborundum,  and 
these  came  in  durability  nearest  to  those  prepared  of  car¬ 
borundum,  but  the  binding  paste  gave  way  much  more 
quickly  in  the  diamond  buttons  :  this,  however,  I  attrib¬ 
uted  to  the  size  and  irregularity  of  the  grains  of  the  dia¬ 
mond. 

It  was  of  interest  to  find  whether  carborundum  possesses 
the  quality  of  phosphorescence.  One  is,  of  course,  prepared 
to  encounter  two  difficulties:  first,  as  regards  the  rough 
product,  the  “crystals,”  they  are  good  conducting,  and 
it  is  a  fact  that  conductors  do  not  phosphoresce  ;  second, 
the  powder,  being  exceedingly  fine,  would  not  be  apt  to 
exhibit  very  prominently  this  quality,  since  we  know  that 
when  crystals,  even  such  as  diamond  or  ruby,  are  finely 
powdered,  they  lose  the  property  of  phosphorescence  to  a 
considerable  degree. 

The  question  presents  itself  here,  can  a  conductor  phos¬ 
phoresce  ?  What  is  there  in  such  a  body  as  a  metal,  for  in¬ 
stance,  that  would  deprive  it  of  the  quality  of  phosphores¬ 
cence,  unless  it  is  that  property  which  characterizes  it  as  a 


80 


conductor?  for  it  is  a  fact  that  most  of  the  phosphorescent 
bodies  lose  that  quality  when  they  are  sufficiently  heated 
to  become  more  or  less  conducting.  Then,  if  a  metal  be  in 
a  large  measure,  or  perhaps  entirely  ,  deprived  of  that  prop¬ 
erty,  it  should  be  capable  of  phosphorescence.  Therefore 
it  is  quite  possible  that  at  some  extremely  high  frequency, 
when  behaving  practically  as  a  non-conductor,  a  metal  or 
any  other  conductor  might  exhibit  the  quality  of  phos¬ 
phorescence,  even  though  it  be  entirely  incapable  of  phos¬ 
phorescing  under  the  impact  of  a  low-frequency  discharge. 
There  is,  however,  another  possible  way  how  a  conductor 
might  at  least  appear  to  phosphoresce. 

Considerable  doubt  still  exists  as  to  what  really  is  phos¬ 
phorescence,  and  as  to  whether  the  various  phenomena 
comprised  under  this  head  are  due  to  the  same  causes. 
Suppose  that  in  an  exhausted  bulb,  under  the  molecular 
impact,  the  surface  of  a  piece  of  metal  or  other  conductor 
is  rendered  strongly  luminous,  but  at  the  same  time  it  is 
found  that  it  remains  comparatively  cool,  would  not  this 
luminosity  be  called  phosphorescence  ?  Now  such  a  result, 
theoretically  at  least,  is  possible,  for  it  is  a  mere  question 
of  potential  or  speed.  Assume  the  potential  of  the  elec¬ 
trode,  and  consequently  the  speed  of  the  projected  atoms, 
to  be  sufficiently  high,  the  surface  of  the  metal  piece 
against  which  the  atoms  are  projected  would  be  rendered 
highly  incandescent,  since  the  process  of  heat  generation 
would  be  incomparably  faster  than  that  of  radiating  or 
conducting  away  from  the  surface  of  the  collision.  In  the 
eye  of  the  observer  a  single  impact  of  the  atoms  would 
cause  an  instantaneous  flash,  but  if  the  impacts  were  re- 


90 


peated  with  sufficient  rapidity  they  would  produce  a  con¬ 
tinuous  impression  upon  his  retina.  To  him  then  the  sur¬ 
face  of  the  metal  would  appear  continuously  incandescent 
and  of  constant  luminous  intensity ,  while  in  reality  the  light 
would  be  either  intermittent  or  at  least  changing  periodically 
in  intensity.  The  metal  piece  would  rise  in  temperature 
until  equilibrium  was  attained — that  is, until  the  energy  con¬ 
tinuously  radiated  would  equal  that  intermittently  sup¬ 
plied.  But  the  supplied  energy  might  under  such  condi¬ 
tions  not  be  sufficient  to  bring  the  body  to  any  more  than 
a  very  moderate  mean  temperature,  especially  if  the  fre¬ 
quency  of  the  atomic  impacts  be  very  low — just  enough 
that  the  fluctuation  of  the  intensity  of  the  light  emitted 
could  not  be  detected  by  the  eye.  The  body  would  now, 
owing  to  the  manner  in  which  the  energy  is  supplied,  emit 
a  strong  light,  and  yet  be  at  a  comparatively  very  low 
mean  temperature.  How  could  the  observer  call  the  lu¬ 
minosity  thus  produced  ?  Even  if  ilie  analysis  of  the  light 
would  teach  him  something  definite,  still  he  would  prob¬ 
ably  rank  it  under  the  phenomena  of  phosphorescence.  It 
is  conceivable  that  in  such  a  way  both  conducting  and  non¬ 
conducting  bodies  may  be  mainiained  at  a  certain  lumin¬ 
ous  intensity,  but  the  energy  required  would  very  greatly 
vary  with  the  nature  and  properties  of  the  bodies. 

These  and  some  foregoing  remarks  of  a  speculative  na¬ 
ture  were  made  merely  to  bring  out  curious  features  of 
alternate  currents  or  electric  impulses.  By  their  help  we 
may  cause  a  body  to  emit  more  light,  while  at  a  certain 
mean  temperature,  than  it  would  emit  if  brought  to  that 
temperature  by  a  steady  supply;  and,  again,  we  may  bring 


91 


a  body  to  the  point  of  fusion,  and  cause  it  to  emit  less 
light  than  when  fused  by  the  application  of  energy  in 
ordinary  ways.  It  all  depends  on  how  we  supply  the 
energy,  and  what  kind  of  vibrations  we  set  up:  in  one  case 
the  vibrations  are  more,  in  the  other  less,  adapted  to  affect 
our  sense  of  vision. 

Some  effects,  which  I  had  not  observed  before,  obtained 
with  carborundum  in  the  first  trials,  I  attributed  to  phos¬ 
phorescence,  but  in  subsequent  experiments  it  appeared 
that  it  was  devoid  of  that  quality.  The  crystals  possess  a 
noteworthy  feature.  In  a  bulb  provided  with  a  single 
electrode  in  the  shape  of  a  small  circular  metal  disc,  for 
instance,  at  a  certain  degree  of  exhaustion  the  electrode  is 
covered  with  a  milky  film,  which  is  separated  by  a  dark 
space  from  the  glow  filling  the  bulb.  When  the  metal  disc 
is  covered  with  carborundum  crystals,  the  film  is  far  more 
intense,  and  snow-white.  This  I  found  later  to  be  merely 
an  effect  of  the  bright  surface  of  the  crystals,  for  when  an 
aluminium  electrode  was  highly  polished  it  exhibited  more 
or  less  the  same  phenomenon.  I  made  a  number  of  ex¬ 
periments  with  the  samples  of  crystals  obtained,  princi¬ 
pally  because  it  would  have  been  of  special  interest  to  find 
that  they  are  capable  of  phosphorescence,  on  account  of 
their  being  conducting.  I  could  not  produce  phosphores¬ 
cence  distinctly,  but  I  must  remark  that  a  decisive  opinion 
cannot  be  formed  until  other  experimenters  have  gone  over 
the  same  ground. 

The  powder  behaved  in  some  experiments  as  though  it 
contained  alumina,  but  it  did  not  exhibit  with  sufficient 
distinctness  the  red  of  the  latter.  Its  dead  color  brightens 


92 


considerably  under  the  molecular  impact,  but  I  am  now 
convinced  it  does  not  phosphoresce.  Still,  the  tests  with  the 
powder  are  not  conclusive,  because  powdered  carborundum 
probably  does  not  behave  like  a  phosphorescent  sulphide, 
for  example,  which  could  be  finely  powdered  without  im¬ 
pairing  the  phosphorescence,  but  rather  like  powdered  ruby 
or  diamond,  and  therefore  it  would  be  necessary,  in  order 
to  make  a  decisive  test,  to  obtain  it  in  a  large  lump  and 
polish  up  the  surface. 

If  the  carborundum  proves  useful  in  connection  with 
these  and  similar  experiments,  its  chief  value  wall  be  found 
in  the  production  of  coatings,  thin  conductors,  buttons,  or 
other  electrodes  capable  of  withstanding  extremely  high 
degrees  of  heat. 

The  production  of  a  small  electrode  capable  of  withstand¬ 
ing  enormous  temperatures  I  regard  as  of  the  greatest  im¬ 
portance  in  the  manufacture  of  light.  It  would  enable  us 
to  obtain,  by  means  of  currents  of  very  high  frequencies, 
certainly  20  times,  if  not  more,  the  quantity  of  light  which 
is  obtained  in  the  present  incandescent  lamp  by  the  same 
expenditure  of  energy.  This  estimate  may  appear  to  many 
exaggerated,  but  in  reality  I  think  it  is  far  from  being  so. 
As  this  statement  might  be  misunderstood  I  think  it  neces¬ 
sary  to  expose  clearly  the  problem  with  which  in  this  line 
of  work  -we  are  confronted,  and  the  manner  in  which,  in 
my  opinion,  a  solution  will  be  arrived  at. 

Any  one  who  begins  a  study  of  the  problem  will  be  apt 
to  think  that  what  is  wanted  in  a  lamp  with  an  electrode 
is  a  very  high  degree  of  incandescence  of  the  electrode. 
There  he  will  be  mistaken.  The  high  incandescence  of 


93 


the  button  is  a  necessary  evil,  but  what  is  really  wanted  is 
the  high  incandescence  of  the  gas  surrounding  the  button. 
In  other  words,  the  problem  in  such  a  lamp  is  to  bring  a 
mass  of  gas  to  the  highest  possible  incandescence.  The 
higher  the  incandescence,  the  quicker  the  mean  vibration, 
the  greater  is  the  economy  of  the  light  production.  But 
to  maintain  a  mass  of  gas  at  a  high  degree  of  incandes¬ 
cence  in  a  glass  vessel,  it  will  al  ways  be  necessary  to  keep 
the  incandescent  mass  away  from  the  glass  ;  that  is,  to 
confine  it  as  much  as  possible  to  the  central  portion  of  the 
globe. 

In  one  of  the  experiments  this  evening  a  brush  was  pro¬ 
duced  at  the  end  of  a  wire.  This  brush  was  a  flame,  a 
source  of  heat  and  light.  It  did  not  emit  much  perceptible 
heat,  nor  did  it  glow  with  an  intense  light;  but  is  it  the  less 
a  flame  because  it  does  not  scorch  my  hand  ?  Is  it  the  less 
a  flame  because  it  does  not  hurt  my  eye  by  its  brilliancy  ? 
The  problem  is  precisely  to  produce  in  the  bulb  such  a 
flame,  much  smaller  in  size,  but  incomparably  more  power¬ 
ful.  Were  there  means  at  hand  for  producing  electric  im¬ 
pulses  of  a  sufficiently  high  frequency,  and  for  transmitting 
them,  the  bulb  could  be  done  away  with,  unless  it  were 
used  to  protect  the  electrode,  or  to  economize  the  energy 
by  confining  the  heat.  But  as  such  means  are  not  at  dis¬ 
posal,  it  becomes  necessary  to  place  the  terminal  in  a  bulb 
and  rarefy  the  air  in  the  same.  This  is  done  merely  to  en¬ 
able  the  apparatus  to  perform  the  work  which  it  is  not 
capable  of  performing  at  ordinary  air  pressure.  In  the 
bulb  we  are  able  to  intensify  the  action  to  any  degree — so 
far  that  the  brush  emits  a  powerful  light. 


94 


The  intensity  of  the  light  emitted  depends  principally  on 
the  frequency  and  potential  of  the  impulses,  and  on  the 
electric  density  on  the  surface  of  the  electrode.  It  is  of  the 
greatest  importance  to  employ  the  smallest  possible  button, 
in  order  to  push  the  density  very  far.  Under  the  violent 
impact  of  the  molecules  of  the  gas  surrounding  it,  the 
small  electrode  is  of  course  brought  to  an  extremely  high 
temperature,  but  around  it  is  a  mass  of  highly  incandescent 
gas,  a  flame  photosphere,  many  hundred  times  the  volume 
of  the  electrode.  With  a  diamond,  carborundum  or  zir- 
conia  button  the  photosphere  can  be  as  much  as  one  thou¬ 
sand  times  the  volume  of  the  button.  Without  much 
reflecting  one  would  think  that  in  pushing  so  far  the  in¬ 
candescence  of  the  electrode  it  would  be  instantly  volatil¬ 
ized.  But  after  a  careful  consideration  he  would  find  that, 
theoretically,  it  should  not  occur,  and  in  this  fact — which, 
however,  is  experimentally  demonstrated — lies  principally 
the  future  value  of  such  a  lamp. 

At  first,  when  the  bombardment  begins,  most  of  the  work 
is  performed  on  the  surface  of  the  button,  but  when  a 
highly  conducting  photosphere  is  formed  the  button  is 
comparatively  relieved.  The  higher  the  incandescence  of 
the  photosphere  the  more  it  approaches  in  conductivity  to 
that  of  the  electrode,  and  the  more,  therefore,  the  solid  and 
the  gas  form  one  conducting  body.  The  consequence  is 
that  the  further  is  forced  the  incandescence  the  more 
work,  comparatively,  is  performed  on  the  gas,  and  the  less 
on  the  electrode.  The  formation  of  a  powerful  photo¬ 
sphere  is  consequently  the  very  means  for  protecting  the 
electrode.  This  protection,  of  course,  is  a  relative  one, 


95 


and  it  should  not  be  thought  that  by  pushing  the  incandes¬ 
cence  higher  the  electrode  is  ac:uallyless  deteriorated, 
Still,  theoretically,  with  extreme  frequencies,  this  result 
must  be  reached,  but  probably  at  a  temperature  too  high 
for  most  of  the  refractory  bodies  known.  Given,  then,  an 
electrode  which  can  withstand  to  a  very  high  limit  the 
effect  of  the  bombardment  and  outward  strain,  it  would 
be  safe  no  matter  how  much  it  is  forced  beyond  that 
limit.  In  an  incandescent  lamp  quite  different  considera¬ 
tions  apply.  There  the  gas  is  not  at  all  concerned:  the 
whole  of  the  work  is  performed  on  the  filament;  and  the 
life  of  the  lamp  diminishes  so  rapidly  with  the  increase  of 
the  degree  of  incandescence  that  economical  reasons  com¬ 
pel  us  to  work  it  at  a  low  incandescence.  But  if  an  incan¬ 
descent  lamp  is  operated  with  currents  of  very  high  fre¬ 
quency,  the  action  of  the  gas  cannot  be  neglected,  and  the 
rules  for  the  most  economical  working  must  be  consider¬ 
ably  modified. 

In  order  to  bring  such  a  lamp  with  one  or  two  electrodes 
to  a  great  perfection,  it  is  necessary  to  employ  impulses  of 
very  high  frequency.  The  high  frequency  secures,  among 
others,  two  chief  advantages,  which  have  a  most  important 
bearing  upon  the  economy  of  the  light  production.  First, 
the  deterioration  of  the  electrode  is  reduced  by  reason  of 
the  fact  that  we  employ  a  great  many  small  impacts,  in¬ 
stead  of  a  few  violent  ones,  which  shatter  quickly  the 
structure;  secondly,  the  formation  of  a  large  photosphere 
is  facilitated. 

In  order  to  reduce  the  deterioration  of  the  electrode  to 
the  minimum,  it  is  desirable  that  the  vibration  be  liar- 


96 


monic,  for  any  suddenness  hastens  the  process  of  destruc¬ 
tion.  An  electrode  lasts  much  longer  when  kept  at  incan¬ 
descence  by  currents,  or  impulses,  obtained  from  a  high- 
frequency  alternator,  which  rise  and  fall  more  or  less 
harmonically,  than  by  impulses  obtained  from  a  disruptive 
discharge  coil.  In  the  latter  case  there  is  no  doubt  that 
most  of  the  damage  is  done  by  the  fundamental  sudden 
discharges. 

One  of  the  elements  of  loss  in  such  a  lamp  is  the  bom¬ 
bardment  of  the  globe.  As  the  potential  is  very  high,  the 
molecules  are  projected  with  great  speed  ;  they  strike  the 
glass,  and  usually  excite  a  strong  phosphorescence.  The 
effect  produced  is  very  pretty,  but  for  economical  reasons 
it  would  be  perhaps  preferable  to  prevent,  or  at  least  re¬ 
duce  to  the  minimum,  the  bombardment  against  the  globe, 
as  in  such  case  it  is,  as  a  rule,  not  the  object  to  excite  phos¬ 
phorescence,  and  as  some  loss  of  energy  results  from  the 
bombardment.  This  loss  in  the  bulb  is  principally  depend¬ 
ent  on  the  potential  of  the  impulses  and  on  the  electric 
density  on  the  surface  of  the  electrode.  In  employing  very 
high  frequencies  the  loss  of  energy  by  the  bombardment 
is  greatly  reduced,  for,  first,  the  potential  needed  to  per¬ 
form  a  given  amount  of  work  is  much  smaller;  and,  sec 
ondly,  by  producing  a  highly  conducting  photosphere 
around  the  electrode,  the  same  result  is  obtained  as  though 
the  electrode  were  much  larger,  which  is  equivalent  to  a 
smaller  electric  density.  But  be  it  by  the  diminution  of 
the  maximum  potential  or  of  the  density,  the  gain  is  ef¬ 
fected  in  the  same  manner,  namely,  by  avoiding  violent 
shocks,  which  strain  the  glass  much  beyond  its  limit  of 


97 


elasticity.  If  the  frequency  could  be  brought  high  enough, 
the  loss  due  to  the  imperfect  elasticity  of  the  glass  would 
be  entirely  negligible.  The  loss  due  to  bombardment  of 
the  globe  may,  however,  be  reduced  by  using  two  elec¬ 
trodes  instead  of  one.  In  such  case  each  of  the  electrodes 
may  be  connected  to  one  of  the  terminals;  or  else,  if  it  is 
preferable  to  use  only  one  wire,  one  electrode  may  be  con¬ 
nected  to  one  terminal  and  the  other  to  the  ground  or  to 
an  insulated  body  of  some  surface,  as,  for  instance,  a  shade 
on  the  lamp.  In  the  latter  case,  unless  some  judgment  is 
used,  one  of  the  electrodes  might  glow  more  intensely  than 
the  other. 

But  on  the  whole  I  find  it*  preferable  when  using  such 
high  frequencies  to  employ  only  one  electrode  and  one  con¬ 
necting  wire.  I  am  convinced  that  the  illuminating  device 
of  the  near  future  will  not  require  for  its  operation  more 
than  one  lead,  and,  at  any  rate,  it  will  have  no  leading-in 
wire,  since  the  energy  required  can  be  as  well  transmitted 
through  the  glass.  In  experimental  bulbs  the  leading-in 
wire  is  most  generally  used  on  account  of  convenience,  as 
in  employing  condenser  coatings  in  the  manner  indicated 
in  Fig.  22,  for  example,  there  is  some  difficulty  in  fitting 
the  parts,  but  these  difficulties  would  not  exist  if  a  great 
many  bulbs  were  manufactured;  otherwise  the  energy  can 
be  conveyed  through  the  glass  as  well  as  through  a  wire, 
and  with  these  high  frequencies  the  losses  are  very  small. 
Such  illuminating  devices  will  necessarily  involve  the  use 
of  very  high  potentials,  and  this,  in  the  eyes  of  practical 
men,  might  be  an  objectionable  feature.  Yet,  in  reality, 
high  potentials  are  not  objectionable  —  certainly  not 


98 


in  the  least  as  far  as  the  safety  of  the  devices  is  con¬ 
cerned. 

There  are  two  ways  of  rendering  an  electric  appliance 
safe.  One  is  to  use  low  potentials,  the  other  is  to  deter¬ 
mine  the  dimensions  of  the  apparatus  so  that  it  is  safe  no 
matter  how  high  a  potential  is  used.  Of  the  two  the  latter 
seems  to  me  the  better  way,  for  then  the  safety  is  absolute,  un¬ 
affected  by  any  possible  combination  of  circumstances  which 
might  render  even  a  low-potential  appliance  dangerous  lo 
life  and  property.  But  the  practical  conditions  require  not 
only  the  judicious  determination  of  the  dimensions  of  the 
apparatus  ;  they  likewise  necessitate  the  employment  of 
energy  of  the  proper  kind.  It  is  easy,  for  instance,  to  con¬ 
struct  a  transformer  capable  of  giving,  when  operated  from 
an  ordinary  alternate  current  machine  of  low  tension,  say 
50,000  volts,  which  might  be  required  to  light  a  highly  ex¬ 
hausted  phosphorescent  tube,  so  that,  in  spite  of  the  high 
potential,  it  is  perfectly  safe,  the  shock  from  it  producing 
no  inconvenience.  Still,  such  a  transformer  would  be  ex¬ 
pensive,  and  in  itself  inefficient;  and,  besides,  what  energy 
was  obtained  from  it  would  not  be  economically  used  for 
the  production  of  light.  The  economy  demands  the  em¬ 
ployment  of  energy  in  the  form  of  extremely  rapid 
vibrations.  The  problem  of  producing  light  has 
been  likened  to  that  of  maintaining  a  certain  high- 
pitch  note  by  means  of  a  bell.  It  should  be  said  a  barely 
audible  note;  and  even  these  words  would  not  express  it,  so 
wonderful  is  the  sensitiveness  of  the  eye.  We  may  deliver 
powerful  blows  at  long  intervals,  waste  a  good  deal  of  energy, 
and  still  not  get  what  we  want;  or  we  may  keep  up  the  note 


99 


by  delivering  frequent  gentle  taps,  and  get  nearer  to  the 
object  sought  by  the  expenditure  of  much  less  energy.  In 
the  production  of  light,  as  far  as  the  illuminating  device  is 
concerned,  there  can  be  only  one  rule — that  is,  to  use  as  high 
frequencies  as  can  be  obtained;  but  the  means  for  the  pro¬ 
duction  and  conveyance  of  impulses  of  such  character  im¬ 
pose,  at  present  at  least,  great  limitations.  Once  it  is  decided 
to  use  very  high  frequencies,  the  return  wire  becomes  un¬ 
necessary,  and  all  the  appliances  are  simplified.  By  the  use 
of  obvious  means  the  same  result  is  obtained  as  though  the 
return  wire  were  used.  It  is  sufficient  for  this  purpose  to 
bring  in  contact  with  the  bulb,  or  merely  in  the  vicinity  of 
the  same,  an  insulated  body  of  some  surface.  The  surface 
need,  of  course,  be  the  smaller,  the  higher  the  frequency 
and  potential  used,  and  necessarily,  also,  the  higher  the 
economy  of  the  lamp  or  other  device. 

This  plan  of  working  has  been  resorted  to  on  several  oc¬ 
casions  this  evening.  So,  for  instance,  when  the  incandes¬ 
cence  of  a  button  was  produced  by  grasping  the  bulb  with 
the  hand,  the  body  of  the  experimenter  merely  served  to 
intensify  the  action.  The  bulb  used  was  similar  to  that  il¬ 
lustrated  in  Fig.  19,  and  the  coil  was  excited  to  a  small  po¬ 
tential,  not  sufficient  to  bring  the  button  to  incandescence 
when  the  bulb  was  hanging  from  the  wire  ;  and  incident¬ 
ally,  in  order  to  perform  the  experiment  in  a  more  suitable 
manner,  the  button  was  taken  so  large  that  a  perceptible 
time  had  to  elapse  before,  upon  grasping  the  bulb,  it  could 
be  rendered  incandescent.  The  contact  with  the  bulb  was, 
of  course,  quite  unnecessary.  It  is  easy,  by  using  a  rather 
large  bulb  with  an  exceedingly  small  electrode,  to  adjust 


100 


the  conditions  so  that  the  latter  is  brought  to  bright  incan¬ 
descence  by  the  mere  approach  of  the  experimenter  within 


Fig.  24.— Bulb  Without  Leading-In  Wire,  Showing 
Effect  of  Projected  Matter. 

a  few  feet  of  the  bulb,  and  that  the  incandescence  subsides 
upon  his  receding. 


101 


In  another  experiment,  when  phosphorescence  was  ex¬ 
cited,  a  similar  bulb  was  used.  Here  again,  originally,  the 
potential  was  not  sufficient 
to  excite  phosphorescence 
until  the  action  was  intensi¬ 
fied — in  this  case,  however? 
to  present  a  different  feature, 
by  touching  the  socket  with 
a  metallic  object  held  in  the 
hand.  The  electrode  in  the 
bulb  was  a  carbon  button  so 
large  that  it  could  not  be 
brought  to  incandescence, 
and  thereby  spoil  the  effect 
produced  by  phosphores¬ 
cence. 

Again,  in  another  of  the 
early  experiments,  a  bulb 
was  used  as  illustrated  in 
Fig.  12.  In  this  instance,  by 
touching  the  bulb  with  one 
or  two  fingers,  one  or  two 
shadows  of  the  stem  inside 
were  projected  against  the 
glass,  the  touch  of  the  fin¬ 
ger  producing  the  same 
result  as  the  application  Fig.  25.— Improved  Experi- 
of  an  external  negative  mental  Bulb. 

electrode  under  ordinary  circumstances. 

In  all  these  experiments  the  action  was  intensified  by 


102 


•  • 

augmenting  the  capacity  at  the  end  of  the  lead  connected 
to  the  terminal.  As  a  rule,  it  is  not  necessary  to  resort  to 
such  means,  and  would  be  quite  unnecessary  with  still 
higher  frequencies  ;  but  when  it  is  desired,  the  bulb,  or 
tube,  can  be  easily  adapted  to  the  purpose. 

Iu  Fig.  24,  for  example,  an  experimental  bulb  L  is  shown, 
which  is  provided  with  a  neck  n  on  the  top  for  the  appli¬ 
cation  of  an  external  tinfoil  coating,  which  may  be  con¬ 
nected  to  a  body  of  larger  surface.  Such  a  lamp  as  illus- 


Fig.  26.— Improved  Bulb  with  Intensifying  Reflector. 

trated  in  Fig.  25  may  also  be  lighted  by  connecting  the  tin- 
foil  coating  on  the  neck  n  to  the  terminal,  and  the  leading- 
in  wire  w  to  an  insulated  plate.  If  the  bulb  stands  in  a 
socket  upright,  as  shown  in  the  cut,  a  shade  of  conducting 
material  may  be  slipped  in  the  neck  n,  and  the  action  thus 
magnified. 

A  more  perfected  arrangement  used  in  some  of  these 
bulbs  is  illustrated  in  Fig.  26.  In  this  case  the  construction 


IDS 

0 

of  the  bulb  is  as  shown  and  described  before,  when  refer¬ 
ence  was  made  to  Fig.  19.  A  zinc  sheet  Z,  with  a  tubular 
extension  T,  is  slipped  over  the  metallic  socket  S.  The 
bulb  hangs  downward  from  the  teiminal  t,  the  zinc  sheet 


Fig.  27.— Phosphorescent  Tube  with  Intensifying 

Reflector. 

Z,  performing  the  double  office  of  intensifier  and  reflector. 
The  reflector  is  separated  from  the  terminal  t  by  an  exten¬ 
sion  of  the  insulating  plug  P. 

A  similar  disposition  with  a  phosphorescent  tube  is  illus- 


104 


strated  in  Fig.  27.  The  tube  T  is  prepared  from  two  short 
tubes  of  a  different  diameter,  which  are  sealed  on  the  ends. 
On  the  lower  end  is  placed  an  outside  conducting  coating 
C,  which  connects  to  the  wire  w.  The  wire  has  a  hook  on 
the  upper  end  for  suspension,  and  passes  through  the  centre 
of  the  inside  tube,  which  is  filled  with  some  good  and 
tightly  packed  insulator.  On  the  outside  of  the  upper  end 
of  the  tube  Tis  another  conducting  coating  Cu  upon  which 
is  slipped  a  metallic  reflector  Z,  which  should  be  separated 
by  a  thick  insulation  from  the  end  of  wire  w. 

The  economical  use  of  such  a  reflector  or  intensifier  would 
require  that  all  energy  supplied  to  an  air  condenser  should 
be  recoverable,  or,  in  other  words,  that  there  should  not  be 
any  losses,  neither  in  the  gaseous  medium  nor  through  its 
action  elsewhere.  This  is  far  from  being  so,  but,  fortu¬ 
nately,  the  losses  may  be  reduced  to  anything  desired.  A  few 
remarks  are  necessary  on  this  subject,  in  order  to  make  the 
experiences  gathered  in  the  course  of  these  investigations 
perfectly  clear. 

Suppose  a  small  helix  with  many  well  insulated  turns,  as 
in  experiment  Fig.  17,  has  one  of  its  ends  connected  to  one 
of  the  terminals  of  the  induction  coil,  and  the  other  to  a 
metal  plate,  or,  for  the  sake  of  simplicity,  a  sphere,  insu¬ 
lated  in  space.  When  the  coil  is  set  to  work,  the  potential 
of  the  sphere  is  alternated,  and  the  small  helix  now  be¬ 
haves  as  though  its  free  end  were  connected  to  the  other 
terminal  of  the  induction  coil.  If  an  iron  rod  be  held 
within  the  small  helix  it  is  quickly  brought  to  a  high  tem¬ 
perature,  indicating  the  passage  of  a  strong  current  through 
the  helix.  How  does  the  insulated  sphere  act  in  this  case  ? 


105 


It  can  be  a  condenser,  storing  and  returning  the  energy 
supplied  to  it,  or  it  can  be  a  mere  sink  of  energy,  and  the 
conditions  of  the  experiment  determine  whether  it  is  more 
one  or  the  other.  The  sphere  being  charged  to  a  high  po¬ 
tential,  it  acts  inductively  upon  the  surrounding  air,  or 
whatever  gaseous  medium  there  might  be.  The  mole¬ 
cules,  or  atoms,  which  are  near  the  sphere  are  of  course 
more  attracted,  and  move  through  a  greater  distance  than 
the  farther  ones.  When  the  nearest  molecules  strike  the 
sphere  they  are  repelled,  and  collisions  occur  at  all  distances 
within  the  inductive  action  of  the  sphere.  It  is  now  clear 
that,  if  the  potential  be  steady,  but  little  loss  of  energy  can 
be  caused  in  this  way,  for  the  molecules  which  are  nearest 
to  the  sphere,  having  had  an  additional  charge  imparted  to 
them  by  contact,  are  not  attracted  until  they  have  parted,  if 
not  with  all,  at  least  with  most  of  the  additional  charge,  which 
can  be  accomplished  only  after  a  great  many  collisions. 
From  the  fact  that  with  a  steady  potential  there  is  but  little 
loss  in  dry  air,  one  must  come  to  such  a  conclusion.  When 
the  potential  of  the  sphere,  instead  of  being  steady,  is  alter¬ 
nating,  the  conditions  are  entirely  different.  In  this  case  a 
rhythmical  bombardment  occurs,  no  matter  whether  the 
molecules  after  coming  in  contact  with  the  sphere  lose  the 
imparted  charge  or  not;  what  is  more,  if  the  charge  is  not 
lost,  the  impacts  are  only  the  more  violent.  Still  if  the 
frequency  of  the  impulses  be  very  small,  the  loss  caused  by 
the  impacts  and  collisions  would  not  be  serious  unless  the 
potential  were  excessive.  But  when  extremely  high  frequen¬ 
cies  and  more  or  less  high  potentials  are  used,  the  loss  may  be 
very  great.  The  total  energy  lost  per  unit  of  time  is  propor- 


106 


tionate  to  the  product  of  the  number  of  impacts  per  second, 
or  the  frequency  and  the  energy  lost  in  each  impact.  But 
the  energy  of  an  impact  must  be  proportionate  to  the  square 
of  the  electric  density  of  the  sphere,  since  the  charge  im¬ 
parted  to  the  molecule  is  proportionate  to  that  density.  I 
conclude  from  this  that  the  total  energy  lost  must  be  propor¬ 
tionate  to  the  product  of  the  frequency  and  the  square  of 
the  electric  density  ;  but  this  law  needs  experimental  con¬ 
firmation.  Assuming  the  preceding  considerations  to  be 
true,  then,  by  rapidly  alternating  the  potential  of  a  body  im¬ 
mersed  in  an  insulating  gaseous  medium,  any  amount  of 
energy  may  be  dissipated  into  space.  Most  of  that  energy 
then,  I  believe,  is  not  dissipated  in  the  form  of  long  ether 
waves,  propagated  to  considerable  distance,  as  is  thought 
most  generally,  but  is  consumed — in  the  case  of  an  insulated 
sphere,  for  example — in  impact  and  collisional  losses — that 
is,  heat  vibrations — on  the  surface  and  in  the  vicinity  of 
the  sphere.  To  reduce  the  dissipation  it  is  necessary  to 
work  with  a  small  electric  density—  the  smaller  the  higher 
the  frequency. 

But  since,  on  the  assumption  before  made,  the  loss  is 
diminished  with  the  square  of  the  density,  and  since  cur¬ 
rents  of  very  high  frequencies  involve  considerable  waste 
when  transmitted  through  conductors,  it  follows  that,  on 
the  whole,  it  is  better  to  employ  one  wire  than  two. 
Therefore,  if  motors,  lamps,  or  devices  of  any  kind  are 
perfected,  capable  of  being  advantageously  operated  by 
currents  of  extremely  high  frequency,  economical  reasons 
will  make  it  advisable  to  use  only  one  wire,  especially  if 
the  distances  are  great. 


107 


Wlien  energy  is  absorbed  in  a  condenser  the  same  be¬ 
haves  as  though  its  capacity  were  increased.  Absorption 
always  exists  more  or  less,  but  generally  it  is  small  and  of 
no  consequence  as  long  as  the  frequencies  are  not  very 
great.  In  using  extremely  high  frequencies,  and,  neces¬ 
sarily  in  such  case,  also  high  potentials,  the  absorption — 
or,  what  is  here  meant  more  particularly  by  this  term,  the 
loss  of  energy  due  to  the  presence  of  a  gaseous  medium — is 
an  important  factor  to  be  considered,  as  the  energy  absorbed 
in  the  air  condenser  may  be  any  fraction  of  the  supplied 
energy.  This  would  seem  to  make  it  very  difficult  to  tell  from 
the  measured  or  computed  capacity  of  an  air  condenser  its 
actual  capacity  or  vibration  period,  especially  if  the  con¬ 
denser  is  of  very  small  surface  and  is  charged  to  a  very  high 
potential.  As  many  important  results  are  dependent  upon 
the  correctness  of  the  estimation  of  the  vibration  period, 
this  subject  demands  the  most  careful  scrutiny  of  other  in¬ 
vestigators.  To  reduce  the  probable  error  as  much  as 
possible  in  experiments  of  the  kind  alluded  to,  it  is 
advisable  to  use  spheres  or  plates  of  large  surface, 
so  as  to  make  the  density  exceedingly  small. 
Otherwise,  when  it  is  practicable,  an  oil  condenser  should 
be  used  in  preference.  In  oil  or  other  liquid  dielectrics 
there  are  seemingly  no  such  losses  as  in  gaseous  media.  It 
being  impossible  to  exclude  entirely  the  gas  in  condensers 
with  solid  dielectrics,  such  condensers  should  be  immersed 
in  oil,  for  economical  reasons  if  nothing  else;  they  can  then 
be  strained  to  the  utmost  and  will  remain  cool.  In  Leyden 
jars  the  loss  due  to  air  is  comparatively  small,  as  the  tin- 
foil  coatings  are  large,  close  together,  and  the  charged 


108 


surfaces  not  directly  exposed;  but  when  the  potentials  are 
very  high,  the  loss  may  be  more  or  less  considerable  at,  or 
near,  the  upper  edge  of  the  foil,  where  the  air  is  princi¬ 
pally  acted  upon.  If  the  jar  be  immersed  in  boiled-out  oil, 
it  will  be  capable  of  performing  four  times  the  amount  of 
work  which  it  can  for  any  length  of  time  when  used  in  the 
ordinary  way,  and  the  loss  will  be  inappreciable. 

It  should  not  be  thought  that  the  loss  in  heat  in  an  air 
condenser  is  necessarily  associated  with  the  formation  of 
visible  streams  or  brushes.  If  a  small  electrode,  inclosed 
in  an  unexhausted  bulb,  is  connected  to  one  of  the  ter¬ 
minals  of  the  coil,  streams  can  be  seen  to  issue  from  the 
electrode  and  the  air  in  the  bulb  is  heated;  if,  instead  of  a 
small  electrode,  a  large  sphere  is  inclosed  in  the  bulb,  no 
streams  are  observed,  still  the  air  is  heated. 

Nor  should  it  be  thought  that  the  temperature  of  an  air 
condenser  would  give  even  an  approximate  idea  of  the 
loss  in  heat  incurred,  as  in  such  case  heat  must  be  given 
off  much  more  quickly,  since  there  is,  in  addition  to  the 
ordinary  radiation,  a  very  active  carrying  away  of  heat  by 
independent  carriers  going  on,  and  since  not  only  the  ap¬ 
paratus,  but  the  air  at  some  distance  from  it  is  heated  in 
consequence  of  the  collisions  which  must  occur. 

Owing  to  this,  in  experiments  with  such  a  coil,  a  rise  of 
temperature  can  be  distinctly  observed  only  when  the  body 
connected  to  the  coil  is  very  small.  But  with  apparatus  on 
a  larger  scale,  even  a  body  of  considerable  bulk  would  be 
heated,  as,  for  instance,  the  body  of  a  person  ;  and  I  think 
that  skilled  physicians  might  make  observations  of  utility 
in  such  experiments,  which,  if  the  apparatus  were 


109 


judiciously  designed,  would  not  present  the  slightest 
danger. 

A  question  of  some  interest,  principally  to  meteorologists, 
presents  itself  here.  How  does  the  earth  behave  ?  The 
earth  is  an  air  condenser,  but  is  it  a  perfect  or  a  very  im¬ 
perfect  one — a  mere  sink  of  energy  ?  There  can  be  little 
doubt  that  to  such  small  disturbance  as  might,  be  caused  in 
an  experiment  the  earth  behaves  as  an  almost  perfect  con¬ 
denser.  But  it  might  be  different  when  its  charge  is  set  in 
vibration  by  some  sudden  disturbance  occurring  in  the 
heavens.  In  such  case,  as  before  stated,  probably  only 
little  of  the  energy  of  the  vibrations  set  up  would  be  lost 
into  space  in  the  form  of  long  ether  radiations,  but  most  of 
the  energy,  I  think,  would  spend  itself  in  molecular  im¬ 
pacts  and  collisions,  and  pass  off  into  space  in  the  form  of 
short  heat,  and  possibly  light,  waves.  As  both  the  fre¬ 
quency  of  the  vibrations  of  the  charge  and  the  potential  are 
in  all  probability  excessive,  the  energy  converted  into  heat 
may  be  considerable.  Since  the  density  must  be  unevenly 
distributed,  either  in  consequence  of  the  irregularity  of  the 
earth’s  surface,  or  on  account  of  the  condition  of  the  at¬ 
mosphere  in  various  places,  the  effect  produced  would  ac¬ 
cordingly  vary  from  place  to  place.  Considerable  varia¬ 
tions  in  the  temperature  and  pressure  of  the  atmosphere 
may  in  this  manner  be  caused  at  any  point  of  the  surface 
of  the  earth.  The  variations  may  be  gradual  or  very  sud¬ 
den,  according  to  the  nature  of  the  general  disturbance, 
and  may  produce  rain  and  storms,  or  locally  modify  the 
weather  in  any  way. 

From  the  remarks  before  made  one  may  see  what  an  im- 


110 


portant  factor  of  loss  the  air  in  tlie  neighborhood  of  a 

charged  surface  becomes  when  the  electric  density  is  great 

and  the  frequency  of  the  impulses  excessive.  But  the 

action  as  explained  implies  that  the  air  is  insulating — that 

is,  that  it  is  composed  of  independent  carriers  immersed  in 

an  insulating  medium.  This  is  the  case  only  when  the  air 

is  at  something  like  ordinary  or  greater,  or  at  extremely 

small,  pressure.  When  the  air  is  slightly  rarefied  and  con 

ducting,  then  true  conduction  losses  occur  also.  In  such  case, 

of  course,  considerable  energy  may  be  dissipated  into  space 

\ 

even  with  a  steady  potential,  or  with  impulses  of  low  fre¬ 
quency,  if  the  density  is  very  great. 

When  the  gas  is  at  very  low  pressure,  an  electrode  is 
heated  more  because  higher  speeds  can  be  reached.  If  the 
gas  around  the  electrode  is  strongly  compressed,  the  dis¬ 
placements,  and  consequently  the  speeds,  are  very  small, 
and  the  heating  is  insignificant.  But  if  in  such  case  the 
frequency  could  be  sufficiently  increased,  the  electrode 
would  be  brought  to  a  high  temperature  as  well  as  if  the 
gas  were  at  very  low  pressure;  in  fact,  exhausting  the  bulb 
is  only  necessary  because  we  cannot  produce  (and  possibly 
not  convey)  currents  of  the  required  frequency. 

Returning  to  the  subject  of  electrode  lamps,  it  is  ob¬ 
viously  of  advantage  in  such  a  lamp  to  confine  as  much  as 
possible  the  heat  to  the  electrode  by  preventing  the  circula¬ 
tion  of  the  gas  in  the  bulb.  If  a  very  small  bulb  be  taken, 
it  would  confine  the  heat  better  than  a  large  one,  but  it 
might  not  be  of  sufficient  capacity  to  be  operated  from  the 
coil,  or,  if  so,  the  glass  might  get  too  hot.  A  simple  way 
to  improve  in  this  direction  is  to  employ  a  globe  of  the  re- 


Ill 


quired  size,  but  to  place  a  small  bulb,  the  diameter  of  which 
is  properly  estimated,  over  the  refractory  button  contained 
in  the  globe.  This  arrangement  is  illustrated  in  Fig.  28. 
The  globe  L  has  in  this  case  a  large  neck  n,  allowing 


Fig.  28.— Lamp  with  Auxiliary  Bulb  for  Confining  the 

Action  to  the  Centre. 

the  small  bulb  6  to  slip  through.  Otherwise  the  construc¬ 
tion  is  the  same  as  shown  in  Fig.  18,  for  example.  The 
small  bulb  is  conveniently  supported  upon  the  stem  s,  car- 


112 


rying  the  refractory  button  m.  It  is  separated  from  the 
aluminium  tube  a  by  several  layers  of  mica  M,  in  order 
to  prevent  the  cracking  of  the  neck  by  the  rapid  heating  of 
the  aluminium  tube  upon  a  sudden  turning  on  of  the  cur¬ 
rent.  The  inside  bulb  should  be  as  small  as  possible  when 
it  is  desired  to  obtain  light  only  by  incandescence  of  the 
electrode.  If  it  is  desired  to  produce  phosphorescence,  the 
bulb  should  be  larger,  else  it  would  be  apt  to  get  too  hot, 
and  the  phosphorescence  would  cease.  In  this  arrange¬ 
ment  usually  only  the  small  bulb  shows  phosphorescence, 
as  there  is  practically  no  bombardment  against  the  outer 
globe.  In  some  of  these  bulbs  constructed  as  illustrated  in 
Fig.  28  the  small  tube  was  coated  with  phosphorescent 
paint,  and  beautiful  effects  were  obtained.  Instead  of  mak- 
'  ing  the  inside  bulb  large,  in  order  to  avoid  undue  heating, 
it  answers  the  purpose  to  make  the  electrode  m  larger.  In 
this  case  the  bombardment  is  weakened  by  reason  of  the 
smaller  electric  density. 

Many  bulbs  were  constructed  on  the  plan  illustrated  in 
Fig.  29.  Here  a  small  bulb  b,  containing  the  refractory 
button  vi,  upon  being  exhausted  to  a  very  high  degree  was 
sealed  in  a  large  globe  L,  which  was  then  moderately  ex¬ 
hausted  and  sealed  off.  The  principal  advantage  of  this  con¬ 
struction  was  that  it  allowed  of  reaching  extremely  high 
vacua,  and,  at  the  same  time  use  a  large  bulb.  It  was  found, 
in  the  course  of  experiences  with  bulbs  such  as  illustrated  in 
Fig.  29,  that  it  was  well  to  make  the  stem  s  near  the  seal 
at  e  very  thick,  and  the  leading-in  wire  w  thin,  as  it  oc¬ 
curred  sometimes  that  the  stem  at  e  was  heated  and  the 
bulb  was  cracked,  Often  the  outer  globe  L  was  exhausted 


113 


only  just  enough  to  allow  the  discharge  to  pass  through, 
and  the  space  between  the  bulbs  appeared  crimson,  pro 
ducing  a  curious  effect.  In  some  cases,  when  the  exhaus¬ 
tion  in  globe  L  was  very  low,  and  the  air  good  conducting, 
it  was  found  necessary,  in  order  to  bring  the  button  m  to 


Fig.  29.— Lamp  with  Independent  Auxiliary  Bulb. 

high  incandescence,  to  place,  preferably  on  the  upper  part 
of  the  neck  of  the  globe,  a  tinfoil  coating  which  was  con¬ 
nected  to  an  insulated  body,  to  the  ground,  or  to  the  other 
terminal  of  the  coil,  as  the  highly  conducting  air  weak- 


114 


ened  the  effect  somewhat,  probably  by  being  acted  upon 
inductively  from  the  wire  w,  where  it  entered  the  bulb  at 
e.  Another  difficulty — which,  however,  is  always  present 
when  the  refractory  button  is  mounted  in  a  very  small  bulb 
— existed  in  the  construction  illustrated  in  Fig.  29,  namely, 
the  vacuum  in  the  bulb  b  would  be  impaired  in  a  com¬ 
paratively  short  time. 

The  chief  idea  in  the  two  last  described  constructions  was 
to  confine  the  heat  to  the  central  portion  of  the  globe  by 
preventing  the  exchange  of  air.  An  advantage  is  secured, 
but  owing  to  the  heating  of  the  inside  bulb  and  slow  evap¬ 
oration  of  the  glass  the  vacuum  is  hard  to  maintain,  even 
if  the  construction  illustrated  in  Fig.  28  be  chosen,  in 
which  both  bulbs  communicate. 

But  by  far  the  better  way — the  ideal  way— would  be  to  reach 
sufficiently  high  frequencies.  The  higher  the  frequency 
the  slower  would  be  the  exchange  of  the  air,  and  I  think 
that  a  frequency  may  be  reached  at  which  there  would  be 
no  exchange  whatever  of  the  air  molecules  around  the  ter¬ 
minal.  We  would  then  produce  a  flame  in  which  there 
would  be  no  carrying  away  of  material,  and  a  queer  flame’ 
it  would  be,  for  it  would  be  rigid  !  With  such  high  fre¬ 
quencies  the  inertia  of  the  particles  would  come  into  play. 
As  the  brush,  or  flame,  would  gain  rigidity  in  virtue  of  the 
inertia  of  the  particles,  the  exchange  of  the  latter  would 
be  prevented.  This  would  necessarily  occur,  for,  the  num¬ 
ber  of  the  impulses  being  augmented,  the  potential  energy 
of  each  would  diminish,  so  that  finally  only  atomic  vibra¬ 
tions  could  be  set  up,  and  the  motion  of  translation  through 
measurable  space  would  cease.  Thus  an  ordinary  gas  burner 


115 


connected  to  a  source  of  rapidly  alternating  potential  might 
have  its  efficiency  augmented  to  a  certain  limit,  and  this  for 
two  reasons — because  of  the  additional  vibration  imparted, 
and  because  of  a  slowing  down  of  the  process  of  carrying 
off.  But  the  renewal  being  rendered  difficult,  and  renewal 
being  necessary  to  maintain  the  burner,  a  continued  in¬ 
crease  of  the  frequency  of  the  impulses,  assuming  they 
could  be  transmitted  to  and  impressed  upon  the  flame, 
would  result  in  the  “  extinction  ”  of  the  latter,  meaning  by 
this  term  only  the  cessation  of  the  chemical  process. 

I  think,  however,  that  in  the  case  of  an  electrode  im¬ 
mersed  in  a  fluid  insulating  medium,  and  surrounded  by 
independent  carriers  of  electric  charges,  which  can  be  acted 
upon  inductively,  a  sufficiently  high  frequency  of  the  im¬ 
pulses  would  probably  result  in  a  gravitation  of  the  gas  all 
around  toward  the  electrode.  For  this  it  would  be  only 
necessary  to  assume  that  the  independent  bodies  are 
irregularly  shaped;  they  would  then  turn  toward  the  elec¬ 
trode  their  side  of  the  greatest  electric  density,  and  this 
would  be  a  position  in  which  the  fluid  resistance  to  ap¬ 
proach  would  be  smaller  than  that  offered  to  the  receding. 

The  general  opinion,  I  do  not  doubt,  is  that  it  is  out  of  the 
question  to  reach  any  such  frequencies  as  might — assuming 
some  of  the  views  before  expressed  to  be  true — produce  any 
of  the  results  which  1  have  pointed  out  as  mere  possibilities. 
This  may  be  so,  but  in  the  course  of  these  investigations, 
from  the  observation  of  many  phenomena  I  have  gained 
the  conviction  that  these  frequencies  would  be  much  lower 
than  one  is  apt  to  estimate  at  first.  In  a  flame  we  set  up 
light  vibrations  by  causing  molecules,  or  atoms,  to  collide. 


ne 


But  wliat  is  the  ratio  of  the  frequency  of  the  collisions  and 
that  of  the  vibrations  set  up  ?  Certainly  it  must  be  incom¬ 
parably  smaller  than  that  of  the  knocks  of  the  bell  and  the 
sound  vibrations,  or  that  of  the  discharges  and  the  oscilla¬ 
tions  of  the  condenser.  We  may  cause  the  molecules  of  the 
gas  to  collide  by  the  use  of  alternate  electric  impulses  of 
high  frequency,  and  so  we  may  imitate  the  process  in  a 
flame  ;  and  from  experiments  with  frequencies  which  we 
are  now  able  to  obtain,  I  think  tha ;  the  result  is  producible 
wflth  impulses  which  are  transmissible  through  a  con¬ 
ductor. 

In  connection  with  thoughts  of  a  similar  nature,  it  ap¬ 
peared  to  me  of  great  interest  to  demonstrate  the  rigidity 
of  a  vibrating  gaseous  column.  Although  with  such  low 
frequencies  as,  say  10,000  per  second,  which  I  was  able  to 
obtain  without  difficulty  from  a  specially  constructed 
alternator,  the  task  looked  discouraging  at  first,  I  made  a 
series  of  experiments.  The  trials  with  air  at  ordinary  press¬ 
ure  led  to  no  result,  but  with  air  moderately  rarefied  I 
obtain  what  I  think  to  be  an  unmistakable  experimental 
evidence  of  the  property  sought  for.  As  a  result  of  this 
kind  might  lead  able  investigators  to  conclusions  of  im¬ 
portance  I  will  describe  one  of  the  experiments  performed. 

It  is  well  known  that  when  a  tube  is  slightly  exhausted 
the  discharge  may  be  passed  through  it  in  the  form  of  a 
thin  luminous  thread.  When  produced  with  currents  of  low 
frequency,  obtained  from  a  coil  operated  as  usual,  this 
thread  is  inert.  If  a  magnet  be  approached  to  it,  the  part 
near  the  same  is  attracted  or  repelled,  according  to  the  di¬ 
rection  of  the  lines  of  force  of  the  magnet.  It  occurred  to 


11? 

me  that  if  such  a  thread  would  be  produced  with  currents 
of  very  high  frequency,  it  should  be  more  or  less  rigid,  and 
as  it  was  visible  it  could  be  easily  studied.  Accordingly  I 
prepared  a  tube  about  1  inch  in  diameter  and  1  metre  long, 
with  outside  coating  at  each  end.  The  tube  was  exhausted 
to  a  point  at  which  by  a  little  working  the.  thread  discharge 
could  be  obtained.  It  must  be  remarked  here  that  the 
general  aspect  of  the  tube,  and  the  degree  of  exhaus¬ 
tion,  are  quite  different  than  wThen  ordinary  low  fre¬ 
quency  currents  are  used.  As  it  was  found  prefer¬ 
able  to  work  with  one  terminal,  the  tube  prepared 
was  suspended  from  the  end  of  a  wire  connected  to  the 
terminal,  the  tinfoil  coating  being  connected  to  the  wire, 
and  to  the  lower  coating  sometimes  a  small  insulated 
plate  was  attached.  When  the  thread  was  formed  it  ex¬ 
tended  through  the  upper  part  of  the  tube  and  lost  itself  in 
the  lower  end.  If  it  possessed  rigid  ty  it  resembled,  not 
exactly  an  elastic  cord  stretched  tight  between  two  sup¬ 
ports,  but  a  cord  suspended  from  a  height  with  a  small 
weight  attache!  at  the  end.  When  the  finger  or  a  magnet 
was  approached  to  the  upper  end  of  the  luminous  thread,  it 
could  be  brought  locally  out  of  position  by  electrostatic  or 
magnetic  action  ;  and  when  the  disturbing  object  was  very 
quickly  removed,  an  analogous  result  was  produced,  as 
though  a  suspended  cord  would  be  displaced  and  quickly 
released  near  the  point  of  suspension.  In  doing  this  the 
luminous  thread  was  set  in  vibration,  and  two  very  sharply 
marked  nodes,  and  a  third  indistinct  one,  were  formed. 
The  vibration,  once  set  up,  continued  for  fully  eight 
minutes,  dying  gradually  out.  The  speed  of  the  vibration 


118 


often  varied  perceptibly,  and  it  could  be  observed  that 
the  electrostatic  attraction  of  the  glass  affected  the 
vibrating  thread ;  but  it  was  clear  that  the  electro¬ 
static  action  was  not  the  cause  of  the  vibration,  for 
the  thread  was  most  generally  stationary,  and  could 
always  be  set  in  vibration  by  passing  the  finger  quickly 
near  the  upper  part  of  the  tube.  With  a  magnet  the 
thread  could  be  split  in  two  and  both  parts  vibrated.  By 
approaching  the  hand  to  the  lower  coating  of  the  tube, 
or  insulated  plate  if  attached,  the  vibration  was  quickened; 
also,  as  far  as  I  could  see,  by  raising  the  potential  or  fre¬ 
quency.  Thus,  either  increasing  the  frequency  or  passing 
a  stronger  discharge  of  the  same  frequency  corresponded  to 
a  tightening  of  the  cord.  I  did  not  obtain  any  experimental 
evidence  with  condenser  discharges.  A  luminous  band  ex¬ 
cited  in  a  bulb  by  repeated  discharges  of  a  Leyden  jar  must 
possess  rigidity,  and  if  deformed  and  suddenly  released 
should  vibrate.  But  probably  the  amount  of  vibrating  mat¬ 
ter  is  so  small  that  in  spite  of  the  extreme  speed  the  inertia 
cannot  prominently  assert  itself.  Besides,  the  observation 
in  such  a  case  is  rendered  extremely  difficult  on  account  of 
the  fundamental  vibration. 

The  demonstration  of  the  fact— which  still  needs  better 
experimental  confirmation — that  a  vibrating  gaseous  col¬ 
umn  possesses  rigidity,  might  greatly  modify  the  views  of 
thinkers.  When  with  low  frequencies  and  insignificant 
potentials  indications  of  that  property  may  be  noted,  how 
must  a  gaseous  medium  behave  under  the  influence  of  enor¬ 
mous  electrostatic  stresses  which  may  be  active  in  the  inter¬ 
stellar  space,  and  which  may  alternate  with  inconceivable 


119 


rapidity?  The  existence  of  such  an  electrostatic,  rhyth¬ 
mically  throbbing  force— of  a  vibrating  electrostatic  field— 
would  show  a  possible  way  how  solids  might  have  formed 
from  the  ultra-gaseous  uterus,  and  how  transverse  and  all 
kinds  of  vibrations  may  be  transmitted  through  a  gaseous 
medium  filling  all  space.  Then,  ether  might  be  a  true 
fluid,  devoid  of  rigidity,  and  at  rest,  it  being  merely  neces¬ 
sary  as  a  connecting  link  (o  enable  interaction.  What  de¬ 
termines  the  rigidity  of  a  body  ?  It  must  be  the  speed  and 
the  amount  of  moving  matter.  In  a  gas  the  speed  may  be 
considerable,  but  the  density  is  exceedingly  small  ;  in  a 
liquid  the  speed  would  be  likely  to  be  small,  though  the 
density  may  be  considerable  ;  and  in  both  cases  the  inertia 
resistance  offered  to  displacement  is  practically  nil.  But 
place  a  gaseous  (or  liquid)  column  in  an  intense,  rapidly 
alternating  electrostatic  field,  set  the  particles  vibrating 
with  enormous  speeds,  then  the  inertia  resistance  asserts  it¬ 
self.  A  body  might  move  with  more  or  less  freedom  through 
the  vibrating  mass,  but  as  a  whole  it  would  be  rigid. 

There  is  a  subject  which  I  must  mention  in  connection 
with  these  experiments  :  it  is  that  of  high  vacua.  This  is  a 
subject  the  study  of  which  is  not  only  interesting,  but  use¬ 
ful,  for  it  may  lead  to  results  of  great  practical  importance. 
In  commercial  apparatus,  such  as  incandescent  lamps, 
operated  from  ordinary  systems  of  distribution,  a  much 
higher  vacuum  than  obtained  at  present  would  not  secure  a 
very  great  advantage.  In  such  a  case  the  work  is  performed 
on  the  filament  and  the  gas  is  little  concerned;  the  improve¬ 
ment,  therefore,  would  be  but  trifling.  But  when  we  be¬ 
gin  to  use  very  high  frequencies  and  potentials,  the  action 


120 


of  the  gas  becomes  all  important,  and  the  degree  of  exhaus¬ 
tion  materially  modifies  the  results.  As  long  as  ordinary 
coils,  even  very  large  ones,  were  used,  the  study  of  the 
subject  was  limited,  because  just  at  a  point  when  it  became 
most  interesting  it  had  to  be  interrupted  on  account  of  the 
“non-striking”  vacuum  being  reached.  But  presently  we 
are  able  to  obtain  from  a  small  disruptive  discharge 
coil  potentials  much  higher  than  even  the  largest  coil 
was  capable  of  giving,  and,  what  is  more,  we  can  make  the 
potential  alternate  with  great  rapidity.  Both  of  these  results 
enable  us  now  to  pass  a  luminous  discharge  through  almost 
any  vacua  obtainable,  and  the  field  of  our  investigations  is 
greatly  extended.  Think  we  as  we  may,  of  all  the  possible 
directions  to  develop  a  practical  illuminant,  the  line  of  high 
vacua  seems  to  be  the  most  promising  at  present.  But  to 
reach  extreme  vacua  the  appliances  must  be  much  more 
improved,  and  ultimate  perfection  will  not  be  attained 
until  we  shall  have  discarded  the  mechanical  and  perfected 
an  electrical  vacuum  pump.  Molecules  and  atoms  can  be 
thrown  out  of  a  bulb  under  the  action  of  an  enormous 
potential :  this  will  be  the  principle  of  the  vacuum  pump 
of  the  future.  For  the  present,  we  must  secure  the  best 
results  we  can  with  mechanical  appliances.  In  this  respect, 
it  might  not  be  out  of  the  way  to  say  a  few  words  about 
the  method  of,  and  apparatus  for,  producing  excessively 
high  degrees  of  exhaustion  of  which  I  have  availed  myself 
in  the  course  of  these  investigations.  It  is  very  probable 
that  other  experimenters  have  used  similar  arrange¬ 
ments  ;  but  as  it  is  possible  that  there  may  be  an  item 
of  interest  in  their  description,  a  few  remarks,  which 


121 

will  render  this  investigation  more  complete,  might  be  per¬ 
mitted. 

The  apparatus  is  illustrated  in  a  drawing  shown  in  Fig. 
30.  S  represents  a  Sprengel  pump,  which  has  been 


Fig.  30.— Apparatus  Used  for  Obtaining  High  Degrees 

of  Exhaustion. 

specially  constructed  to  better  suit  the  work  required.  The 
stop-cock  which  is  usually  employed  has  been  omitted,  and 
instead  of  it  a  hollow  stopper  s  has  been  fitted  in  the  neck 


of  the  reservoir  R.  This  stopper  has  a  small  hole  h, 
through  which  the  mercury  descends;  the  size  of  the  outlet 
o  being  properly  determined  with  respect  to  the  section  of 
the  fall  tube  t,  'which  is  sealed  to  the  reservoir  instead  of 
being  connected  to  it  in  the  usual  manner.  This  arrange¬ 
ment  overcomes  the  imperfections  and  troubles  which  often 
arise  from  the  use  of  the  stopcock  on  the  reservoir  and  the 
connection  of  die  latter  with  the  fall  tube. 

The  pump  is  connected  through  a  U-shaped  tube  t  to  a 
very  large  reservoir  Rx.  Especial  care  was  taken  in  fitting 
the  grinding  surfaces  of  the  stoppers p  and px,  and  both  of 
these  and  the  mercury  caps  above  them  were  made  excep¬ 
tionally  long.  After  the  U-shaped  tube  was  fitted  and  put 
in  place,  it  was  heated,  so  as  to  soften  and  take  off  the 
strain  resulting  from  imperfect  fitting.  The  U-shaped  tube 
was  provided  with  a  stopcock  C,  and  two  ground  connec¬ 
tions  g  and  gx — one  for  a  small  bulb  b,  usually  containing 
caustic  potash,  and  the  other  for  the  receiver  r,  to  be 
exhausted. 

The  reservoir  Rx  was  connected  by  means  of  a  rubber 
tube  to  a  slightly  larger  reservoir  R2,  each  of  the  two 
reservoirs  being  provided  with  a  stopcock  Cx  and  C2,  re¬ 
spectively.  The  reservoir  R2  could  be  raised  and  lowered 
by  a  wheel  and  rack,  and  the  range  of  its  motion  was  so 
determined  that  when  it  was  filled  with  mercury  and  the 
stopcock  C2  closed,  so  as  to  form  a  Torricellian  vacuum  in 
it  when  raised,  it  could  be  lifted  so  high  that  the  mercury 
in  reservoir  Rx  would  stand  a  little  above  stopcock  Cx ; 
and  when  this  stopcock  was  closed  and  the  reservoir 
R2  descended,  so  as  to  form  a  Torricellian  vacuum  in 


123 


reservoir  R^  it  could  be  lowered  so  far  as  to  completely 
empty  the  latter,  the  mercury  filling  the  reservoir  Rs  up 
to  a  little  above  stopcock  C2. 

The  capacity  of  the  pump  and  of  the  connections  was 
taken  as  small  as  possible  relatively  to  the  volume  of  reser¬ 
voir,  Rlt  since,  of  course,  the  degree  of  exhaustion  depend¬ 
ed  upon  the  ratio  of  these  quantities. 

With  this  apparatus  I  combined  the  usual  means  indi¬ 
cated  by  former  experiments  for  the  production  of  very 
high  vacua.  In  most  of  the  experiments  it  was  convenient 
to  use  caustic  potash.  I  may  venture  to  say,  in  regard  to 
its  use,  that  much  time  is  saved  and  a  more  perfect  action 
of  the  pump  insured  by  fusing  and  boiling  the  potash  as 
soon  as,  or  even  before,  the  pump  settles  down.  If  this 
course  is  not  followed  the  sticks,  as  ordinarily  employed, 
may  give  moisture  off  at  a  certain  very  slow  rate,  and  the 
pump  may  work  for  many  hours  without  reaching  a  very 
high  vacuum.  The  potash  was  heated  either  by  a  spirit 
lamp  or  by  passing  a  discharge  through  it,  or  by  passing  a 
current  through  a  wire  contained  in  it.  The  advantage  in 
the  latter  case  was  that  the  heating  could  be  more  rapidly 
repeated. 

Generally  the  process  of  exhaustion  was  the  following: — 
At  the  start,  the  stop-cocks  C  and  being  open,  and  all 
other  connections  closed,  the  reservoir  R»  was  raised  so  far 
that  the  mercury  filled  the  reservoir  Rt  and  a  part  of  the 
narrow  connecting  U-shaped  tube.  When  the  pump  was 
set  to  work,  the  mercury  would,  of  course,  quickly  rise  in 
the  tube,  and  reservoir  R2  was  lowered,  the  experimenter 
keeping  the  mercury  at  about  the  same  level.  The  reser- 


124 


voir  R2  was  balanced  by  a  long  spring  which  facilitated  the 
operation,  and  the  friction  of  the  parts  was  generally  suf¬ 
ficient  to  keep  it  almost  in  any  position.  When  the  Sprengel 
pump  had  done  its  work,  the  reservoir  R2  was  further 
lowered  and  the  mercury  descended  in  Rl  and  filled  R2, 
whereupon  stopcock  C2  was  closed.  The  air  adhering  to 
the  walls  of  Rt  and  that  absorbed  by  the  mercury  was  car¬ 
ried  off,  and  to  free  the  mercury  of  all  air  the  reservoir  R2 
was  for  a  long  time  worked  up  and  down.  During  this  proc¬ 
ess  some  air,  which  would  gather  below  stopcock  C2,  was 
expelled  from  R2  by  lowering  it  far  enough  and  open¬ 
ing  the  stopcock,  closing  the  latter  again  before 
raising  the  reservoir.  When  all  the  air  had  been 
expelled  from  the  mercury,  and  no  air  would  gather  in 
R2  when  it  was  lowered,  the  caustic  potash  was  resorted  to. 
The  reservoir  R2  was  now  again  raised  until  the  mercury 
in  Rl  stood  above  stopcock  C^.  The  caustic  potash  was 
fused  and  boiled,  and  the  moisture  partly  carried  off  by  the 
pump  and  partly  re-absorbed;  and  this  process  of  heating 
and  cooling  was  repeated  many  times,  and  each  time,  upon 
the  moisture  being  absoibed  or  carried  off,  the  reservoir 
R2  was  for  a  long  time  raised  and  lowered.  In  this  man¬ 
ner  all  the  moisture  was  carried  off  from  the  mercury,  and 
both  the  reservoirs  were  in  proper  condition  to  be  used. 
The  reservoir  R2  was  then  again  raised  to  the  top,  and  the 
pump  was  kept  working  for  a  long  time.  When  the  high¬ 
est  vacuum  obtainable  with  the  pump  had  been  reached 
the  potash  bulb  was  usually  wrapped  with  cotton  which 
was  sprinkled  with  ether  so  as  to  keep  the  potash  at  a  very 
low  temperature,  then  the  reservoir  R2  was  lowered,  and 


125 


upon  reservoir  Rl  being  emptied  the  receiver  r  was  quickly 
sealed  up. 

When  a  new  bulb  was  put  on,  the  mercury  was  always 
raised  above  stopcock  Cl5  which  was  closed,  so  as  to 
always  keep  the  mercury  and  both  the  reservoirs  in  fine 
condition,  and  the  mercury  was  never  withdrawn  from  Rl 
except  when  the  pump  had  reached  the  highest  degree  of 
exhaustion.  It  is  necessary  to  observe  this  rule  if  it  is 
desired  to  use  the  apparatus  to  advantage. 

By  means  of  this  arrangement  I  was  able  to  proceed  very 
quickly,  and  when  the  apparatus  was  in  perfect  order  it  was 
possible  to  reach  the  phosphorescent  stage  in  a  small  bulb 
in  less  than  15  minutes,  which  is  certainly  very  quick  work 
for  a  small  laboratory  arrangement  requiring  all  in  all  about 
100  pounds  of  mercury.  With  ordinary  small  bulbs  the  ratio 
of  the  capacity  of  the  pump,  receiver,  and  connections,  and 
that  of  reservoir  R  was  about  1-20,  and  the  degrees  of  exhaus¬ 
tion  reached  were  necessarily  very  high,  though  I  am  unable 
to  make  a  precise  and  reliable  statement  how  far  the  ex¬ 
haustion  was  carried. 

What  impresses  the  investigator  most  in  the  course  of 
these  experiences  is  the  behavior  of  gases  when  subjected 
to  great  rapidly  alternating  electrostatic  stresses.  But  he 
must  remain  in  doubt  as  to  whether  the  effects  observed 
are  due  wholly  to  the  molecules,  or  atoms,  of  the  gas  which 
chemical  analysis  discloses  to  us,  or  whether  there  enters 
into  play  another  medium  of  a  gaseous  nature,  comprising 
atoms,  or  molecules,  immersed  in  a  fluid  pervading  the 
space.  Such  a  medium  surely  must  exist,  and  I  am  con¬ 
vinced  that ,  for  instance,  even  if  air  were  absent,  the  sur- 


126 


face  and  neighborhood  of  a  body  in  space  would  be  heated 
by  rapidly  alternating  the  potential  of  the  body;  but  no 
such  heating  of  the  surface  or  neighborhood  could  occur  if 
all  free  atoms  were  removed  and  only  a  homogeneous,  in¬ 
compressible,  and  elastic  fluid — such  as  ether  is  supposed  to 
be — would  remain,  for  then  there  would  be  no  impacts,  no 
collisions.  In  such  a  case,  as  far  as  the  body  itself  is  con¬ 
cerned,  only  frictional  losses  in  the  inside  could  occur. 

It  is  a  striking  fact  that  the  discharge  through  a  gas  is 
established  with  ever  increasing  freedom  as  the  frequency 
of  the  impulses  is  augmented.  It  behaves  in  this  respect 
quite  contrarily  to  a  metallic  conductor.  In  the  latter  the 
impedance  enters  prominently  into  play  as  the  frequency 
is  increased,  but  the  gas  acts  much  as  a  series  of  conden¬ 
sers  would:  the  facility  with  which  the  discharge  passes 
through  seems  to  depend  on  the  rate  of  change  of  potential. 
If  it  act  so,  then  in  a  vacuum  tube  even  of  great  length,  and 
no  matter  how  strong  the  current,  self-induction  could  not 
assert  itself  to  any  appreciable  degree.  We  have,  then,  as 
far  as  we  can  now  see,  in  the  gas  a  conductor  which  is  capa¬ 
ble  of  transmitting  electric  impulses  of  any  frequency  which 
we  may  be  able  to  produce.  Could  the  frequency  be  brought 
high  enough,  then  a  queer  system  of  electric  distribution, 
which  would  be  likely  to  interest  gas  companies,  might  be  re¬ 
alized  :  metal  pipes  filled  with  gas — the  metal  being  the  in¬ 
sulator,  the  gas  the  conductor — supplying  phosphorescent 
bulbs,  or  perhaps  devices  as  yet  uninvented.  It  is  certainly 
possible  to  take  a  hollow  core  of  copper,  rarefy  the  gas' in 
the  same,  and  by  passing  impulses  of  sufficiently  high  fre¬ 
quency  through  a  circuit  around  it,  bring  the  gas  inside  to 


127 


a  high  degree  of  incandescence;  but  as  to  the  nature  of  the 
forces  there  would  be  considerable  uncertainty,  for  it  would 
be  doubtful  whether  with  such  impulses  the  copper  core 
would  act  as  a  static  screen.  Such  paradoxes  and  apparent 
impossibilities  we  encounter  at  every  step  in  this  line  of 
work,  and  therein  lies,  to  a  great  extent,  the  cl  aim  of  the 
study. 

I  have  here  a  short  and  wide  tube  which  is  exhausted  to 
a  high  .  degree  and  covered  with  a  substantial  coating  of 
bronze,  the  coating  allowing  barely  the  light  to  shine 
through.  A  metallic  clasp,  with  a  hook  for  suspending  the 
tube,  is  fastened  around  the  middle  portion  of  the  latter, 
the  clasp  being  in  contact  with  the  bronze  coating.  I  now 
want  to  light  the  gas  inside  by  suspending  the  tube  on  a 
wire  connected  to  the  coil.  Any  one  who  would  try  the 
experiment  for  the  first  time,  not  having  any  previous  ex¬ 
perience,  would  probably  take  care  to  be  quite  alone  when 
'  making  the  trial,  for  fear  that  he  might  become  the  joke  of 
his  assistants.  Still,  the  bulb  lights  in  spite  of  the  metal 
.  coating,  and  the  light  can  be  distinctly  perceived 
through  the  latter.  A  long  tube  covered  with  aluminium 
bronze  lights  when  held  in  one  hand — the  other 
touching  the  terminal  of  the  coil — quite  powerfully.  It 
might  be  objected  that  the  coatings  are  not  sufficiently 
conducting  ;  still,  even  if  they  were  highly  resistant,  they 
ought  to  screen  the  gas.  They  ceitainly  screen  it  perfectly 
in  a  condition  of  rest,  but  not  by  far  perfectly  when  the 
charge  is  surging  in  the  coating.  But  the  loss  of  energy 
which  occurs  within  the  tube,  notwithstanding  the  screen, 
is  occasioned  principally  by  the  presence  of  the  gas.  Were 


128 


we  to  take  a  large  hollow  metallic  sphere  and  fill  it  with  a 
perfect  incompressible  fluid  dielectric,  there  would  be  no 
loss  inside  of  the  sphere,  and  consequently  the  inside 
might  be  considered  as  perfectly  screened,  though  the 
potential  be  very  rapidly  alternating.  Even  were  the 
sphere  filled  with  oil,  the  loss  would  be  incomparably 
smaller  than  when  the  fluid  is  replaced  by  a  gas,  for  in  the 
latter  case  the  force  produces  displacements;  that  means 
impact  and  collisions  in  the  inside. 

No  matter  what  the  pressure  of  the  gas  may  be,  it  be¬ 
comes  an  important  factor  in  the  heating  of  a  conductor 
when  the  electric  density  is  great  and  the  frequency  very 
high.  That  in  the  heating  of  conductors  by  lightning  dis¬ 
charges  air  is  an  element  of  great  importance,  is  almost  as 
certain  as  an  experimental  fact.  I  may  illustrate  the 
action  of  the  air  by  the  following  experiment:  I  take  a 
short  tube  which  is  exhausted  to  a  moderate  degree  and  has 
a  platinum  wire  running  through  the  middle  from  one  end 
to  the  other.  I  pass  a  steady  or  low  frequency  current 
through  the  wire,  and  it  is  heated  uniformly  in  all  parts. 
The  heating  here  is  due  to  conduction,  or  frictional  losses, 
and  the  gas  around  the  wire  has — as  far  as  we  can  see — no 
function  to  perform.  But  now  let  me  pass  sudden  dis¬ 
charges,  or  a  high  frequency  current,  through  the  wire. 
Again  the  wire  is  heated,  this  time  principally  on  the  ends 
and  least  in  the  middle  portion;  and  if  the  frequency  of  the 
impulses,  or  the  rate  of  change,  is  high  enough,  the  wire 
might  as  well  be  cut  in  the  middle  as  not,  for  practically 
all  the  heating  is  due  to  the  rarefied  gas.  Here  the 
gas  might  only  act  as  a  conductor  of  no  impedance 


129 


diverting  the  current  from  the  wire  as  the  impedance  of 
the  latter  is  enormously  increased,  and  merely  heating  the 
ends  of  the  wire  by  reason  of  their  resistance  to  the  passage 
of  the  discharge.  But  it  is  not  at  all  necessary  that  the  gas 
in  the  tube  should  be  conducting;  it  might  be  at  an  ex¬ 
tremely  low  pressure,  still  the  ends  cf  the  wire  would  be 
heated — as,  however,  is  ascertained  by  experience — only 
the  two  ends  would  in  such  case  not  be  electrically  con¬ 
nected  through  the  gaseous  medium.  Now  what  with 
these  frequencies  and  potentials  occurs  in  an  exhausted 
tube  occurs  in  the  lightning  discharges  at  ordinary  pressure. 
We  only  need  remember  one  of  the  facts  arrived  at  in  the 
course  of  these  investigations,  namely,  that  to  impulses  of 
very  high  frequency  the  gas  at  ordinary  pressure  behaves 
much  in  the  same  manner  as  though  it  were  at  moderately 
low  pressure.  I  think  that  in  lightning  discharges  fre¬ 
quently  wires  or  conducting  objects  are  volatilized  merely 
because  air  is  present,  and  that,  were  the  conductor  im¬ 
mersed  in  an  insulating  liquid,  it  would  be  safe,  for  then 
the  energy  would  have  to  spend  itself  somewhere  else. 
From  the  behavior  of  gases  to  sudden  impulses  of  high  po¬ 
tential  I  am  led  to  conclude  that  there  can  be  no  surer  way 
of  diverting  a  lightning  discharge  than  by  affording  it  a 
passage  through  a  volume  of  gas,  if  such  a  thing  can  be 
done  in  a  practical  manner. 

There  are  two  more  features  upon  which  I  think  it  neces¬ 
sary  to  dwell  in  connection  with  these  experiments— the 
“  radiant  state  ”  and  the  “  non-striking  vacuum.” 

Any  one  who  has  studied  Crookes’  work  must  have  re¬ 
ceived  the  impression  that  the  “  radiant  state  ”  is  a  property 


130 


of  the  gas  inseparably  connected  with  an  extremely  high 
degree  of  exhaustion.  But  it  should  be  remembered  that 
the  phenomena  observed  in  an  exhausted  vessel  are  limited 
to  the  character  and  capacity  of  the  apparatus  which  is 
made  use  of.  I  think  that  in  a  bulb  a  molecule,  or  atom, 


Fig.  31.  -Bulb  Showing  Radiant  Lime  Stream  at  Low 

Exhaustion. 

does  not  precisely  move  in  a  straight  line  because  it  meets 
no  obstacle,  but  because  the  velocity  imparted  to  it  is  suffi¬ 
cient  to  propel  it  in  a  sensibly  straight  line.  The  mean  free 
path  is  one  thing,  but  the  velocity — the  energy  associated 


i3i 


with  the  moving  body — is  another,  and  under  ordinary  cir¬ 
cumstances  I  believe  that  it  is  a  mere  question  of  potential 
or  speed.  A  disruptive  discharge  coil,  when  the  potential 
is  pushed  very  far,  excites  phosphorescence  and  projects 
shadows,  at  comparatively  low  degrees  of  exhaustion.  In 
a  lightning  discharge,  matter  moves  in  straight  lines  at 
ordinary  pressure  when  the  mean  free  path  is"  exceedingly 
small,  and  frequently  images  of  wires  or  other  metallic 
objects  have  been  produced  by  the  particles  thrown  off  in 
straight  lines. 

I  have  prepared  a  bulb  to  illustrate  by  an  experiment 
the  correctness  of  these  assertions.  In  a  globe  L  (Fig.  31, 
I  have  mounted  upon  a  lamp  filament  / a  piece  of  lime  l. 
The  lamp  filament  is  connected  with  a  wire  which  leads 
into  the  bulb,  and  the  general  construction  of  the  latter  is 
as  indicated  in  Fig.  19,  befcie  described.  The  bulb  being 
suspended  from  a  wire  connected  to  the  terminal  of  the 
coil,  and  the  latter  being  set  to  work,  the  lime  piece  Z  and 
the  projecting  parts  of  the  filament  /  are  bombarded.  The 
degree  of  exhaustion  is  just  such  that  with  the  potential 
the  coil  is  capable  of  giving  phosphorescence  of  the  glass 
is  produced,  but  disappears  as  soon  as  the  vacuum  is 
impaired.  The  lime  containing  moisture,  and  moisture 
being  given  off  as  soon  as  heating  occurs,  the  phospho¬ 
rescence  lasts  only  for  a  few  moments.  When  the  lime 
has  been  sufficiently  heated,  enough  moisture  has  been 
given  off  to  impair  materially  the  vacuum  of  the  bulb. 
As  the  bombardment  goes  on,  one  point  of  the  lime  piece 
is  more  heated  than  c,ther  points,  and  the  result  is  that 
finally  practically  all  the  discharge  passes  through  that 


182 


point  which  is  intensely  heated,  and  a  white  stream  of  lime 
particles  (Fig.  31)  then  breaks  forth  from  that  point.  This 
stream  is  composed  of  “  radiant”  matter,  yet  the  degree  of 
exhaustion  is  low.  But  the  particles  move  in  straight  lines 
because  the  velocity  imparted  to  them  is  great,  and  this  is 
due  to  three  causes — to  the  great  electric  density,  the  high 
temperature  of  the  small  point,  and  the  fact  that  the  par¬ 
ticles  of  the  lime  are  easily  torn  and  thrown  off — far  more 
easily  than  those  of  carbon.  With  frequencies  such  as  we 
are  able  to  obtain,  the  particles  are  bodily  thrown  off  and 
projected  to  a  considerable  distance;  but  with  sufficiently 
high  frequencies  no  such  thing  would  occur:  in  such  case 
only  a  stress  would  spread  or  a  vibration  would  be  propa¬ 
gated  through  the  bulb.  It  would  be  out  of  the  question  to 
reach  any  such  frequency  on  the  assumption  that  the 
atoms  move  with  the  speed  of  light;  but  I  believe  that  such 
a  thing  is  impossible;  for  this  an  enormous  potential 
would  be  required.  With  potentials  which  we  are  able  to 
obtain,  even  with  a  disruptive  discharge  coil,  the  speed 
must  be  quite  insignificant. 

As  to  the  “  non-striking  vacuum,”  the  point  to  be  noted 
is  that  it  can  occur  only  with  low  frequency  impulses,  and 
it  is  necessitated  by  the  impossibility  of  carrying  off  enough 
energy  with  such  impulses  in  high  vacuum  since  the  few 
atoms  which  are  around  the  terminal  upon  coming  in  con¬ 
tact  with  the  same  are  repelled  and  kept  at  a  distance  for  a 
comparatively  long  period  of  time,  and  not  enough  work 
can  be  performed  to  render  the  effect  perceptible  to  the 
eye.  If  the  difference  of  potential  between  the  terminals 
is  raised,  the  dielectric  breaks  down.  But  with  very  high 


133 


frequency  impulses  there  is  no  necessity  for  such  breaking 
down,  since  any  amount  of  work  can  be  performed  by  con¬ 
tinually  agitating  the  atoms  in  the  exhausted  vessel,  provided 
the  frequency  is  high  enough.  It  is  easy  to  reach — even 
with  frequencies  obtained  from  an  alternator  as  here  used — 
a  stage  at  which  the  discharge  does  not  pass  between  two 
electrodes  in  a  narrow  tube,  each  of  these  being  connected 
to  one  of  the  terminals  of  the  coil,  but  it  is  difficult  to  reach 
a  point  at  which  a  luminous  discharge  would  not  occur 
around  each  electrode. 

A  thought  which  naturally  presents  itself  in  connection 
with  high  frequency  currents,  is  to  make  use  of  their  pow¬ 
erful  electro-dynamic  inductive  action  to  produce  light 
effects  in  a  sealed  glass  globe.  The  leading-in  wire  is  one 
of  the  defects  of  the  present  incandescent  lamp,  and  if  no 
other  improvement  were  made,  that  imperfection  at  least 
should  be  done  away  with.  Following  this  thought,  I  have 
carried  on  experiments  in  various  directions,  of  which 
some  were  indicated  in  my  former  paper.  I  may  here 
mention  one  or  two  more  lines  of  experiment  which  liave 
been  followed  up. 

Many  bulbs  were  constructed  as  shown  in  Fig.  32  and 
Fig.  83. 

In  Fig.  32  a  wide  tube  T  was  sealed  to  a  smaller  W- 
shaped  tube  U,  of  phosphorescent  glass.  In  the  tube  T 
was  placed  a  coil  C  of  aluminium  wire,  the  ends  of  which 
were  provided  with  small  spheres  t  and  tx  of  aluminium, 
and  reached  into  the  U  tube.  The  tube  T  was  slipped  into 
a  socket  containing  a  primary  coil  through  which 
usually  the  discharges  of  Ley  den  jars  were  directed,  and 


134 


the  rarefied  gas  in  the  small  V  tube  was  excited  to  strong 
luminosity  by  the  high-tension  currents  induced  in  the  coil 
C.  When  Leyden  jar  discharges  were  used  to  induce  cur- 


Fig.  32.— Electro-Dynamic  Fig.  33.  —  Electro-Dynamic 
Induction  Tube.  Induction  Lamp. 

rents  in  the  coil  O,  it  was  found  necessary  to  pack  the  tube 
T  tightly  with  insulating  powder,  as  a  discharge  would 
occur  frequently  between  the  turns  of  the  coil,  especially 


185 


when  the  primary  was  thick  and  the  air  gap,  through 
which  the  jais  discharged,  large,  and  no  little  trouble  was 
experienced  in  this  way. 

In  Fig.  83  is  illustrated  another  form  of  the  bulb  con¬ 
structed.  In  this  case  a  tube  T  is  sealed  to  a  globe  L. 
The  tube  contains  a  coil  C,  the  ends  of  which  pass  through 
two  small  glass  tubes  t  and  tx,  which  are  sealed  to  the 
tube  T.  Two  refractory  buttons  m  and  m±  are  mounted 
on  lamp  filaments  which  are  fastened  to  the  ends  of  the 
wires  passing  through  the  glass  tubes  t  and  tx.  Generally 
in  bulbs  made  on  this  plan  the  globe  L  communicated  with 
the  tube  T.  For  this  purpose  the  ends  of  the  small  tubes 
t  and  tx  were  just  a  trifle  heated  in  the  burner,  merely  to 
hold  the  wires,  but  not  to  interfere  with  the  communica¬ 
tion.  The  tube  T,  with  the  small  tubes,  wires  through  the 
same,  and  the  refractory  buttons  m  and  ml,  was  first  pre¬ 
pared,  and  then  sealed  to  globe  L,  whereupon  the  coil  C 
was  slipped  in  and  the  connections  made  to  its  ends.  The 
tube  was  then  packed  with  insulating  powder,  jamming 
the  latter  as  tight  as  possible  up  to  very  nearly  the  end, 
then  it  was  closed  and  only  a  small  hole  left  through  which 
the  remainder  of  the  powder  was  introduced,  and  finally  the 
end  of  the  tube  was  closed.  Usually  in  bulbs  constructed  as 
shown  in  Fig.  33  an  aluminium  tube  a  was  fastened  to  the 
upper  end  s  of  each  of  the  tubes  t  and  tlt  in  order  to  protect 
that  end  against  the  heat.  The  buttons  m  and  m1  could  be 
brought  to  any  degree  of  incandescence  by  passing  the  dis¬ 
charges  of  Leyden  jars  around  the  coil  C.  In  such  bulbs 
with  two  buttons  a  very  curious  effect  is  produced  by  the 
formation  of  the  shadows  of  each  of  the  two  buttons. 


136 


Another  line  of  experiment,  which  has  been  assiduously 
followed,  was  to  induce  by  electro- dynamic  induction  a 
current  or  luminous  discharge  in  an  exhausted  tube  or  bulb. 
This  matter  has  received  such  able  treatment  at  the 
hands  of  Prof.  J.  J.  Thomson  that  I  could  add  but  little  to 
what  he  has  made  known,  even  had  I  made  it  the  special 
subject  of  this  lecture.  Still,  since  experiences  in  this  line 
have  gradually  led  me  to  the  present  views  and  results,  a 
few  words  must  be  devoted  here  to  this  subject. 

It  has  occurred,  no  doubt,  to  many  that  as  a  vacuum  tube 
is  made  longer  the  electromotive  force  per  unit  length  of 
the  tube,  necessary  to  pass  a  luminous  discharge  through 
the  latter,  gets  continually  smaller;  therefore,  if  the  ex¬ 
hausted  tube  be  made  long  enough,  even  with  low  fre¬ 
quencies  a  luminous  discharge  could  be  induced  in  such  a 
tube  closed  upon  itself.  Such  a  tube  might  be  placed 
around  a  hall  or  on  a  ceiling,  and  at  once  a  simple  ap¬ 
pliance  capable  of  giving  considerable  light  would  be 
obtained.  But  this  would  be  an  appliance  hard  to  manu¬ 
facture  and  extremely  unmanageable.  It  would  not  do  to 
make  the  tube  up  of  small  lengths,  because  there  would 
be  with  ordinary  frequencies  considerable  loss  in  the 
coatings,  and  besides,  if  coatings  wrere  used,  it  would  be 
better  to  supply  the  current  directly  to  the  tube  by  con¬ 
necting  the  coatings  to  a  transformer.  But  even  if  all 
objections  of  such  nature  were  reimned,  still,  with  low  fre¬ 
quencies  the  light  conversion  itself  would  be  inefficient,  as 
I  have  before  stated.  In  using  extremely  high  frequencies 
the  length  of  the  secondary — in  other  words,  the  size  of 
the  vessel— can  be  reduced  as  far  as  desired,  and  the  effi- 


137 


ciency  of  the  light  conversion  is  increased,  provided  that 
means  are  invented  for  efficiently  obtaining  such  high  fre¬ 
quencies.  Thus  one  is  led,  from  theoretical  and  practical 
considerations,  to  the  use  of  high  frequencies,  and  this 
means  high  electromotive  forces  and  small  currents  in  the 
primary.  When  he  works  with  condenser  charges — and 
they  are  the  only  means  up  to  the  present  known  for 
reaching  these  extreme  frequencies — he  gets  to  electro¬ 
motive  forces  of  several  thousands  of  volts  per  turn  of  the 
primary.  He  cannot  multiply  the  electro-dynamic  induct¬ 
ive  effect  by  taking  more  turns  in  the  primary,  for  he  ar¬ 
rives  at  the  conclusion  that  the  best  way  is  to  work  with 
one  single  turn — though  he  must  sometimes  depart  from 
this  rule — and  he  must  get  along  with  whatever  inductive 
effect  he  can  obtain  with  one  turn.  But  before  he  has 
long  experimented  with  the  extreme  frequencies  required 
to  set  up  in  a  small  bulb  an  electromotive  force  of  several 
thousands  of  volts  he  realizes  the  great  importance  of  elec¬ 
trostatic  effects,  and  these  effects  grow  relatively  to  the 
electro-dynamic  in  significance  as  the  frequency  is  in¬ 
creased. 

Now,  if  anything  is  desirable  in  this  case,  it  is  to  increase 
the  frequency,  and  this  would  make  it  still  worse  for  the 
electro-dynamic  effects.  On  the  other  hand,  it  is  easy  to  exalt 
the  electrostatic  action  as  far  as  one  likes  by  taking  more 
turns  on  the  secondary,  or  combining  self-induction  and 
capacity  to  raise  the  potential.  It  should  also  be  remem¬ 
bered  that,  in  reducing  the  current  to  the  smallest  value  and 
increasing  the  potential,  the  electric  impulses  of  high  fre¬ 
quency  can  be  more  easily  transmitted  through  a  conductor. 


138 

These  and  similar  thoughts  determined  me  to  devote 
more  attention  to  the  electrostatic  phenomena,  and  to  en¬ 
deavor  to  produce  potentials  as  high  as  possible,  and  alter¬ 
nating  as  fast  as  they  could  be  made  to  alternate.  I  then 
found  that  I  could  excite  vacuum  tubes  at  considerable 
distance  from  a  conductor  connected  to  a  properly  con¬ 
structed  coil,  and  that  I  could,  by  converting  the  oscilla¬ 
tory  current  of  a  condenser  to  a  higher  potential,  establish 
electrostatic  alternating  fields  which  acted  through  the 
whole  extent  of  a  room,  lighting  up  a  tube  no  matter 
where  it  was  held  in  space.  I  thought  I  recognized  that  I 
had  made  a  step  in  advance,  and  I  have  persevered  in  this 
line;  but  I  wish  to  say  that  I  share  with  all  lovers  cf  science 
and  progress  the  one  and  only  desire — to  reach  a  result  of 
utility  to  men  in  any  direction  to  which  thought  or  experi¬ 
ment  may  lead  me.  I  think  that  this  departure  is  the  right 
one,  for  I  cannot  see,  from  the  observation  of  the  phenom¬ 
ena  which  manifest  themselves  as  the  frequency  is  in¬ 
creased,  what  there  would  remain  to  act  between  two 
circuits  conveying,  for  instance,  impulses  of  several  hundred 
millions  per  second,  except  electrostatic  forces.  Even  with 
such  trifling  frequencies  the  energy  would  be  practically 
all  potential,  and  my  conviction  has  grown  strong  that,  to 
whatever  kind  of  motion  light  may  be  due,  it  is  produced 
by  tremendous  electrostatic  s  resses  vibrating  with  extreme 
rapidity. 

Of  all  these  phenomena  observed  with  currents,  or  electric 
impulses,  of  high  frequency,  the  most  fascinating  for  an 
audience  are  certainly  thos$  which  are  noted  in  an  electro¬ 
static  field  acting  through  considerable  distance,  and  the 


139 


best  an  unskilled  lecturer  can  do  is  to  begin  and  finish  with 
the  exhibition  of  these  singular  effects.  I  take  a  tube  in 
the  hand  and  move  it  about,  and  it  is  lighted  wherever  I 
may  hold  it ;  throughout  space  the  invisible  forces  act. 
But  I  may  take  another  tube  and  it  might  not  light,  the 
vacuum  being  very  high.  I  excite  it  by  means  of  a  dis¬ 
ruptive  discharge  coil,  and  now  it  will  light  in  the  electro¬ 
static  field.  I  may  put  it  away  for  a  few  weeks  or  months, 
still  it  retains  the  faculty  of  being  excited.  What  change 
have  I  produced  in  the  tube  in  the  act  of  exciting  it?  If  a 
motion  imparted  to  the  atoms,  it  is  difficult  to  perceive  how 
it  can  persist  so  long  without  being  arrested  by  frictional 
losses  ;  and  if  a  strain  exerted  in  the  dielectric,  such  as  a 
simple  electrification  would  produce,  it  is  easy  to  see  how 
it  may  persist  indefinitely,  but  very  difficult  to  understand 
why  such  a  condition  should  aid  the  excitation  when  we 
have  to  deal  with  potentials  which  are  rapidly  alternating. 

Since  I  have  exhibited  these  phenomena  for  the  first  time, 
I  have  obtained  some  other  interesting  effects.  For  in¬ 
stance,  I  have  produced  the  incandescence  of  a  button, 
filament,  or  wire  enclosed  in  a  tube.  To  get  to  this  result 
it  was  necessary  to  economize  the  energy  which  is  obtained 
from  the  field  and  direct  most  of  it  on  the  small  body  to  be 
rendered  incandescent.  At  the  beginning  the  task  appeared 
difficult,  but  the  experiences  gathered  permitted  me  to  reach 
the  result  easily.  In  Fig.  34  and  Fig.  35  two  such  tubes 
are  illustrated  which  are  prepared  for  the  occasion.  In  Fig. 
34  a  short  tube  Tx ,  sealed  to  another  long  tube  T,  is  pro¬ 
vided  with  a  stem  s,  with  a  platinum  wire  sealed  in  the 
latter.  A  very  thin  lamp  filament  Z  is  fastened  to  this 


140 


wire,  and  connection  to  the  outside  is  made  through  a  thin 
copper  wire  w.  The  tube  is  provided  with  outside  and 
inside  coatings,  C  and  G\  respectively,  and  is  filled  as  far  as 


Fig.  34.— Tube  with  Fila-  Fig.  35.  —  Crookes’  Experi¬ 
ment  Rendered  Incan-  ment  in  Electrostatic 

DESCENT  IN  AN  ELECTRO  FIELD. 

static  Field. 

the  coatings  reach  with  conducting,  and  the  space  above 
with  insulating  powder.  These  coatings  are  merely  used 
to  enable  me  to  perform  two  experiments  with  the  tube — 


141 


namely,  to  produce  the  effect  desired  either  by  direct  con¬ 
nection  of  the  body  of  the  experimenter  or  of  another  body 
to  the  wire  w,  or  by  acting  inductively  through  the  glass. 
The  stem  sis  provided  with  an  aluminium  tube  a,  for  pur¬ 
poses  before  explained,  and  only  a  small  part  of  the  fila¬ 
ment  reaches  out  of  this  tube.  By  holding  the  tube  T ^  any¬ 
where  in  the  electrostatic  field  the  filament  is  rendered  in¬ 
candescent. 

A  more  interesting  piece  of  apparatus  is  illustrated  in 
Fig.  35.  The  construction  is  the  same  as  before,  only  in¬ 
stead  of  the  lamp  filament  a  small  platinum  wire  p,  sealed 
in  a  stem  s,  and  bent  above  it  in  a  circle,  is  connected  to 
the  copper  wfire  wThich  is  joined  to  an  inside  coating 
C.  A  small  stem  is  provided  with  a  needle,  on  the 
point  of  which  is  arranged  to  rotate  very  freely  a  very  light 
fan  of  mica  v.  To  prevent  the  fan  from  falling  out,  a  thin 
stem  of  glass  g  is  bent  properly  and  fastened  to  the  alu¬ 
minium  tube.  When  the  glass  tube  is  held  anywhere  in  the 
electrostatic  field  the  platinum  wire  becomes  incandescent, 
and  the  mica  vanes  are  rotated  very  fast. 

Intense  phosphorescence  may  be  excited  in  a  bulb  by 
merely  connecting  it  to  a  plate  within  the  field,  and  the 
plate  need  not  be  any  larger  than  an  ordinary  lamp  shade. 
The  phosphorescence  excited  with  these  currents  is  incom¬ 
parably  more  powerful  than  with  ordinary  apparatus.  A 
small  phosphorescent  bulb,  when  attached  to  a  wire  con¬ 
nected  to  a  coil,  emits  sufficient  light  to  allow  reading  or¬ 
dinary  print  at  a  distance  of  five  to  six  paces.  It  was  of 
interest  to  see  how  some  of  the  phosphorescent  bulbs  of 
Professor  Crookes  would  behave  with  these  currents,  and 


142 


he  has  had  the  kindness  to  lend  me  a  few  for  the  occasion. 
The  effects  produced  are  magnificent,  especially  by  the  sul¬ 
phide  of  calcium  and  sulphide  of  zinc.  From  the  disrup¬ 
tive  discharge  coil  they  glow  intensely  merely  by  holding 
them  in  the  hand  and  connecting  the  body  to  the  terminal 
of  tliec  ail. 

To  whatever  results  investigations  of  this  kind  may  lead, 
their  chief  interest  lies  for  the  present  in  the  possibilities 
they  offer  for  the  production  of  an  efficient  illuminating 
device.  In  no  branch  of  electric  industry  is  an  advance 
more  desired  than  in  the  manufacture  of  light.  Every 
thinker,  when  considering  the  barbarous  methods  em¬ 
ployed,  the  deplorable  losses  incurred  in  our  best  systems 
of  light  production,  must  have  asked  himself,  What  is  likely 
to  be  the  light  of  the  future?  Is  it  to  be  an  incandescent 
solid,  as  in  the  present  lamp,  or  an  incandescent  gas,  or  a 
phosphorescent  body,  or  something  like  a  burner,  but  in¬ 
comparably  more  efficient  ? 

There  is  little  chance  to  perfect  a  gas  burner  ;  not,  per¬ 
haps,  because  human  ingenuity  has  been  bent  upon  that 
problem  for  centuries  without  a  radical  departure  having 
been  made  — though  this  argument  is  not  devoid  of  force— 
but  because  in  a  burner  the  higher  vibrations  can  never  be 
reached  except  by  passing  through  all  the  low  ones.  For 
how  is  a  flame  produced  unless  by  a  fall  of  lifted  weights? 
Such  process  cannot  be  maintained  without  renewal,  and 
renewal  is  repeated  passing  from  low  to  high  vibrations. 
One  way  only  seems  to  be  open  to  improve  a  burner,  and 
that  is  by  trying  to  reach  higher  degrees  of  incandescence. 
Higher  incandescence  is  equivalent  to  a  quicker  vibration; 


143 


that  means  more  light  from  the  same  material,  and  that, 
again,  means  more  economy.  In  this  direction  some  im¬ 
provements  have  been  made,  but  the  progress  is  hampered 
by  many  limitations.  Discarding,  then,  the  burner,  there 
remain  the  three  ways  first  mentioned,  which  are  essen¬ 
tially  electrical. 

Suppose  the  light  of  the  immediate  future  to  be  a  solid 
rendered  incandescent  by  electricity.  Would  it  not  seem 
that  it  is  better  to  employ  a  small  button  than  a  frail  fila¬ 
ment  ?  From  many  considerations  it  certainly  must  be 
concluded  that  a  button  is  capable  of  a  higher  economy, 
assuming,  of  course,  the  difficulties  connected  with  the 
operation  of  such  a  lamp  to  be  effectively  overcome.  But 
to  light  such  a  lamp  we  require  a  high  potential  ;  and  to 
get  this  economically  we  must  use  high  frequencies. 

Such  considerations  apply  even  more  to  the  production 
of  light  by  the  incandescence  of  a  gas,  or  by  phosphores¬ 
cence.  In  all  cases  we  require  high  frequencies  and  high 
potentials.  These  thoughts  occurred  to  me  a  long  time  ago. 

Incidentally  we  gain,  by  the  use  of  very  high  frequen¬ 
cies,  many  advantages,  such  as  a  higher  economy  in  the 
light  production,  the  possibility  of  working  with  one  lead, 
the  possibility  of  doing  away  with  the  leading-in  wire,  etc. 

The  question  is,  how  far  can  we  go  with  frequencies  ? 
Ordinary  conductors  rapidly  lose  the  facility  of  transmit¬ 
ting  electric  impulses  when  the  frequency  is  greatly  in¬ 
creased.  Assume  the  means  for  the  production  of  impulses 
of  very  great  frequency  brought  to  the  utmost  perfection, 
every  one  will  naturally  ask  how  to  transmit  them  when 
the  necessity  arises.  In  transmitting  such  impulses  through 


144 


conductors  we  must  remember  that  we  have  to  deal  with 
pressure  and  flow,  in  the  ordinary  interpretation  of  these 
terms.  Let  the  pressure  increase  to  an  enormous  value, 
and  let  the  flow  correspondingly  diminish,  then  such  im¬ 
pulses — variations  merely  of  pressure,  as  it  were — can  no 
doubt  be  transmitted  through  a  wire  even  if  their  frequency 
be  many  hundreds  of  millions  per  second.  It  would,  of 
course,  be  out  of  question  to  transmit  such  impulses 
through  a  wire  immersed  in  a  gaseous  medium,  even  if  the 
wire  were  provided  with  a  thick  and  excellent  insulation 
for  most  of  the  energy  would  be  lost  in  molecular  bom¬ 
bardment  and  consequent  heating.  The  end  of  the  wire 
connected  to  the  source  would  be  heated,  and  the  remote 
end  would  receive  but  a  trifling  part  of  the  energy  sup¬ 
plied.  The  prime  necessity,  then,  if  such  electric  impulses 
are  to  be  used,  is  to  find  means  to  reduce  as  much  as  pos¬ 
sible  the  dissipation. 

The  first  thought  is,  employ  the  thinnest  possible  wire 
surrounded  by  the  thickest  practicable  insulation.  The 
next  thought  is  to  employ  electrostatic  screens.  The  insu¬ 
lation  of  the  wire  may  be  covered  with  a  thin  conducting 
coating  and  the  latter  connected  to  the  ground.  But  this 
would  not  do,  as  then  all  the  energy  would  pass  through 
the  conducting  coating  to  the  ground  and  nothing  would 
get  to  the  end  of  the  wire.  If  a  ground  connection  is  made 
it  can  only  be  made  through  a  conductor  offering  an  enor¬ 
mous  impedance,  or  though  a  condenser  of  extremely  small 
capacity.  This,  however,  does  not  do  away  with  other 
difficulties. 

If  the  wave  length  of  the  impulses  is  much  smaller  than 


145 


the  length  of  the  wire,  then  corresponding  short  waves 
wTill  be  sent  up  in  the  conducting  coating,  and  it  will  be 
more  or  less  the  same  as  though  the  coating  were  directly 
connected  to  earth.  It  is  therefore  necessary  to  cut  up  the 
coating  in  sections  much  shorter  than  the  wavelength. 
Such  an  arrangement  does  not  still  afford  a  perfect  screen, 
but  it  is  ten  thousand  times  better  than  none.  I  think  it 
preferable  to  cut  up  the  conducting  coating  in  small  sec¬ 
tions,  even  if  the  current  waves  be  much  longer  than  the 
coating.  • 

If  a  wire  were  provided  with  a  perfect  electrostatic 
screen,  it  would  be  the  same  as  though  all  objects  were 
removed  from  it  at  infinite  distance.  The  capacity  would 
then  be  reduced  to  the  capacity  of  the  wire  itself,  which 
would  be  very  small.  It  would  then  be  possible  to  send 
over  the  wire  current  vibrations  of  very  high  frequencies 
at  enormous  distance  without  affecting  greatly  the  char¬ 
acter  of  the  vibrations.  A  perfect  screen  is  of  course  out  of 
the  question,  but  I  believe  that  with  a  screen  such  as  I  have 
just  described  telephony  could  be  rendered  practicable 
across  the  Atlantic.  According  to  my  ideas,  the  gutta¬ 
percha  covered  wire  should  be  provided  with  a  third  con¬ 
ducting  coating  subdivided  in  sections.  On  the  top  of 
this  should  be  again  placed  a  layer  of  gutta-percha  and 
other  insulation,  and  on  the  top  of  the  whole  the  armor. 
But  such  cables  will  not  be  constructed,  for  ere  long  in¬ 
telligence-transmitted  without  wires— will  throb  through 
the  earth  like  a  pulse  through  a  living  organism.  The 
wonder  is  that,  with  the  present  state  of  knowledge  and 
the  experiences  gained,  no  attempt  is  being  made  to  dis- 


146 


turb  the  electrostatic  or  magnetic  condition  of  the  earth, 
and  transmit,  if  nothing  else,  intelligence. 

It  has  been  my  chief  aim  in  presenting  these  results  to 
point  out  phenomena  or  features  of  novelty,  and  to  advance 
ideas  which  I  am  hopeful  will  serve  as  starting  points  of 
new  departures.  It  has  been  my  chief  desire  this  evening 
to  entertain  you  with  some  novel  experiments.  Your  ap¬ 
plause,  so  frequently  and  generously  accorded,  has  told  me 
that  I  have  succeeded. 

In  conclusion,  let  me  thank  you  most  heartily  for  your 
kindness  and  attention,  and  assure  you  that  the  honor  I 
have  had  in  addressing  such  a  distinguished  audience,  the 
pleasure  I  have  had  in  presenting  these  results  to  a  gather¬ 
ing  of  so  many  able  men — and  among  them  also  some  of 
those  in  whose  w'ork  for  many  years  past  I  have  found  en¬ 
lightenment  and  constant  pleasure— I  shall  never  forget. 


A  TIMELY  WORK. 


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